1428 GMT: Outside Manchester United's Old Trafford ground fans have been paying tribute to the club's most successful manager -- most seem glum at the news if not totally surprised.
A man wearing a Manchester United shirt with the name 'Sir Alex' on the back is pictured outside the club's Carrington training ground in Manchester, northwest England, on May 8, 2013, following the announcement of manager Sir Alex Ferguson's retirement.
"Basically I have been dreading this day but I knew it had to come one day. [It's a ] bit out of the blue," says Gary Potter, 46.
"I thought he might have a couple of seasons left in him, take it to 30 years at Old Trafford. But to be honest with you, I have respect as he has won everything now."
Graeme Page, 25, from Toronto says his reaction to the news of Ferguson's departure was "one of shock but not one of great surprise.
"There had been a lot of indications this was coming in the past couple of weeks especially with the hip operation and naming the stand after him this year but still a shock, still a shock."
1412 GMT: All of Britain's major bookmakers seem convinced Everton's David Moyes will be the man to step into the United hot-seat -- the most generous odds now available on him are 1/8.
1404 GMT: Former United striker Ole Gunnar Solskjaer has been giving his reaction to Ferguson's departure to United's in-house TV station MUTV:
"He really showed how he appreciated you and you didn't doubt that he trusted you," says the Norwegian striker, who scored 91 goals in 235 appearances for United between 1996 and 2007.
"I will never forget the loyalty he showed me. Everything I have learnt I have learnt from the boss."
1350 GMT: Shares in Manchester United are down round 4.9% in opening trades on the New York Stock Exchange on the news of Ferguson's imminent departure.
1340 GMT: The news of Ferguson's imminent departure has travelled around the world, with Manchester United fans in Bangkok expressing their disappointment at the news.
"I'm shocked and I'm very sad. I still don’t know who will come next and how good he will be," Gun Khamensang tells AFPTV.
"I'm very concerned. I'm afraid it won't be the same without him."
Fellow fan Waranya Phromchai is also downcast at the news.
"I'm sad because he was in charge for 26 years and he left when the team was very strong. I feel bad."
1315 GMT: Michel Platini, president of European football's governing body EUFA, has hailed Ferguson as "a true visionary" who has made "a major contribution" to football.
"His CV is almost unique in a profession where results count and which normally looks to short-term rather than long-term solutions," Platini said.
"His dedication, his attention to details and his eye for talent while manager of Manchester United and Aberdeen have been richly rewarded for over 30 years."
1255 GMT: Ferguson has had a trophy-laden career at United, but his future at the club was reportedly at stake in January 1990 when the team, struggling in the then First Division, travelled to Nottingham Forest for an FA Cup third-round tie.
Luckily for Ferguson a Mark Robins goal took the away side through that day and the Scot never looked back.
Victory over Crystal Palace in an FA Cup final replay that season gave the Scot his first trophy at Old Trafford and sparked an unprecedented run of success that has seen him amass a further 37 honours in his time at the club.
1250 GMT: Old Trafford was a very different place when Ferguson arrived as United's new manager on November 6, 1986, and United were a very different team.
Fourth from bottom in the old English First Division, they had gone 19 years without winning the league and were forced to toil in obscurity while hated rivals Liverpool swept all before them.
1240 GMT: Ferguson's final game in charge of United will be away to West Bromwich Albion on May 19, the club's last Premier League game of the season.
The Scot is due to have a hip replacement operation this summer.
1222 GMT: Here's a summary of developments since the announcement by Manchester United in a statement released at 0815 GMT this morning of Alex Ferguson's plans to retire as their manager at the end of this season.
Rumours and media report of Ferguson's shock retirement only began circulating yesterday, but he said it was a decision he had been considering for some time.
-- "The decision to retire is one that I have thought a great deal about and one that I have not taken lightly. It is the right time," Ferguson said in a statement.
"It was important to me to leave an organisation in the strongest possible shape and I believe I have done so," added Ferguson, who will bow out with United having wrested back the Premier League title this season from local rivals Manchester City
-- Ferguson will remain at United as a director and club ambassador, and said he was confident he was stepping down as manager with the team in good shape
-- United have so far given no indication of a successor, but current Everton manager David Moyes is strong favourite with all of Britain's major high street bookmakers for the post
-- Ferguson, 71, guided United to 13 Premier League titles and two European Champions League crowns in 26 years in charge at Old Trafford
1200 GMT: Former England striker Michael Owen, who was used sparingly by Ferguson in three seasons at United after joining them in 2009, says he feels honoured to have played under the Scot.
"It's just not sinking in! Manchester United with no Sir Alex just doesn't feel right," he writes on his official Twitter account @themichaelowen.
"What a man and great that it has ended on his terms. What a privilege to have played under arguably the best manager the world has ever seen. His record will surely never be eclipsed."
1145 GMT: Former United star Cristiano Ronaldo, now with Real Madrid, keeps it short and sweet on his official Twitter account @Cristiano:
"Thanks for everything, Boss," the Portuguese winger writes, above a youthful picture of himself with Ferguson at Old Trafford, apparently just after he had signed for the club in 2003.
1134 GMT: Former United striker Dwight Yorke has been discussing the possible reasons behind the timing of Ferguson's announcement.
"I think probably the fact of the club floating on the stock market meant this decision needed to come out very quickly," the former Trinidad and Tobago forward tells Sky Sports News.
"But the people within the football club knew this was likely to happen this season. And I think with his hip replacement, with David Gill going as well, that sort of pushed him to say 'this might be the best time for me to retire'.
"It's a shock to the system because he's been there every day. He's the one person when you go into the football club he's always there.
"For him not to be there from the start of next season, it's not going to be right around the football club and it will take some getting used to."
1120 GMT: There's been frenzied activity on the financial and sports betting markets in relation to Ferguson's successor at United, according to British-based spread-betting company Spreadex.
"With David Moyes the favourite to take over from Ferguson, clients have been taking a bearish view on the news, shorting the stock on the New York Stock Exchange ahead of the US market open at 2.30pm," writes Spreadex financial trader Shavaz Dalla.
"Since floating in August last year at $14, the share price has risen to highs of above $19 after United charged to the Premier League title and investors took comfort that the pound sterling24m signing of Robin van Persie had proved good business rather than a risk for an ageing, injury-prone player.
"However, Spreadex clients were this morning taking a view the stock would open below the $18.80 level on the open."
1115 GMT: Scotland's First Minister Alex Salmond has hailed Manchester United manager Alex Ferguson, saying his trophy haul at unfancied Aberdeen proved that he was one of football's all-time great managers.
Salmond has told AFP that while the Scot had won virtually every title available at United, his earlier achievements proved they were not simply down to the English champions' might.
While at Aberdeen between 1978 and 1986, Ferguson managed to break the dominance of Glasgow giants Celtic and Rangers -- who have won every title since.
"He's had a fantastic career," Hearts supporter Salmond said.
"I'm pleased he's managed to catch everyone by surprise because I know he'll be pleased!"
1105 GMT: Reaction via Twitter to the announcement of Ferguson's departure from Chelsea and Arsenal, two London clubs with a long history of rivalry with United.
@ChelseaFC: "All at #CFC would like to wish Sir Alex Ferguson the very best in his retirement. He has been a fantastic adversary over 26 years."
@Arsenal: "Everyone at Arsenal wishes Sir Alex Ferguson health and happiness following the announcement of his retirement as Manchester United manager."
1055 GMT: French striker Louis Saha, who played for United from 2004 to 2008 and is currently with Rome club Lazio, is full of praise for his former boss:
"Wow S A Ferguson leaving. Hope is health ok. He is the most powerful man i ever met in my life after my dad. Huge respect for Football God," Saha wrirtes via his official Twitter handle @louissaha08.
1040 GMT: Everton boss David Moyes has emerged as the early front-runner to replace Alex Ferguson as manager at Manchester United.
Moyes has been linked to the Old Trafford vacancy by British media reports and is currently odds-on favourite for the post with all of Britain's major high street bookmakers.
The Scot has long been spoken of with admiration by his compatriot Ferguson for his work on a tight budget at Everton, but has not won a major trophy since taking charge of the Liverpool-based club in 2002.
Others in the running for the United job include Real Madrid manager Jose Mourinho -- currently second favourite for the job -- who established a friendly rivalry with Ferguson when in charge of Chelsea and has made no secret of his desire to return to England.
1018 GMT: Fifa president Sepp Blatter has given his reaction to Ferguson's departure:
"Just heard Sir Alex Ferguson is retiring at end of season. His achievements in the game place him without doubt as one of the 'greats'. Was honour to present Sir Alex with award at 2011 Ballon D'Or. Will his longevity at the top ever be repeated?"
1011 GMT: Most UK high street bookmakers have slashed the odds on current Everton boss David Moyes becoming the next manager of Manchester United, from around 11/10 40 minutes ago to between 1/4 and 1/8.
The price on Jose Mourinho getting the job has widely drifted out to 7/2 from 6/4 over the same period.
1003 GMT: Vincent Kompany, captain of United's fierce rivals Manchester City, is gracious in his praise of Ferguson:
"Sir Alex, one of the best managers of all time. After 26 years of success in the game, we all owe him a tribute," Kompany posts on @VincentKompany.
1000 GMT: "Disappointed, shocked, sad. Didn't think THAT day would be today," writes former United goalkeeper great Peter Schmeichel of Ferguson's departure via @Pschmeichel.
The Danish goalkeeper who was one of Ferguson's most important signings at United, making 292 appearances for the club after joining them in 1991.
0955 GMT: Former United and England midfielder Paul Ince describes Ferguson as one of a kind and says finding a replacement will not be easy.
Current Blackpool manager Ince told Sky Sports News: "He's done the lot, you will never see anyone of his kind again."
When Ince joined United from West Ham in 1989 Ferguson made sure his move was not ended because of a problem with his medical.
"I remember the first day that I joined Man Utd. I failed my medical and I thought my move to Man Utd was going to collapse. The way he treated me was like a son and I will never forget that moment."
0950 GMT: Ed Miliband, leader of Britain's main opposition Labour party, has also given his reaction to the departure of Ferguson, a lifelong Labour supporter:
"Proud man. Great manager. Staunch Labour Party supporter. Sir Alex Ferguson will never be forgotten," he posts on @Ed_Miliband.
One especially cruel reader @Dan Hose replies: "He's not dead, Ed."
0943 GMT: British Prime Minister David Cameron has praised Ferguson in a post on his official Twitter handle @David_Cameron, though jokingly says hopes the Scot's impending departure will improve the chances of the relegation-threatened Aston Villa side he supports:
"Sir Alex Ferguson’s achievement at MUFC has been exceptional. Hopefully his retirement will make life a little easier for my team AVFC."
0935 GMT: Current Everton manager David Moyes is favourite with most UK high street bookmakers to succeed Ferguson at United, with most of them pricing him at 11/10 to fill the role.
Current Real Madrid and former Chelsea boss Jose Mourinho is widely priced at 6/4 for the job while Borussia Dortmund coach Jurgen Klopp stands between 7/1 and 8/1.
0930 GMT: Joel Glazer, joint chairman of the Manchester United board with brother Avie, says in a statement released by the club that the 2008 Champions League final penalty shootout success over Chelsea was one of the highlights among many memories.
"I will always cherish the wonderful memories he has given us, like that magical night in Moscow."
Avie Glazer said: "I am delighted to announce that Alex has agreed to stay with the Club as a director.
"His contributions to Manchester United over the last 26 years have been extraordinary and, like all United fans, I want him to be a part of its future.”
0920 GMT: Ferguson's managerial career began with Scottish lower league club East Stirlingshire in 1974 and saw him win 49 major trophies in all.
The former Glasgow Rangers' striker forged his reputation in charge of Aberdeen, taking the Dons to a trio of Scottish Premier League titles and the 1983 UEFA Cup' Winners Cup before joining United in 1986.
0916 GMT: Four of the top worldwide trends on Twitter at the moment relate to Ferguson:
#thankyousiralex
#fergieretires
#OldTrafford
And #If Mourinho
0912 GMT: Manchester United chief executive David Gill has said working with Alex Ferguson has been the "greatest experience" of his working life.
Ferguson announced this morning that he will stand down at the end of the season after a 26-year reign at the club, having celebrated his 49th and final piece of silverware with a 13th Premier League title this season.
Gill said: "I've had the tremendous pleasure of working very closely with Alex for 16 unforgettable years - through the treble, the double, countless trophy wins and numerous signings.
"We knew that his retirement would come one day and we both have been planning for it by ensuring the quality of the squad and club structures are in first-class condition.
"Alex's vision, energy and ability have built teams - both on and off the pitch - that his successor can count on as among the best and most loyal in world sport.
"The way he cares for this club, his staff and for the football family in general is something that I admire. It is a side to him that is often hidden from public view but it is something that I have been privileged to witness in the last 16 years.
"What he has done for this club and for the game in general will never be forgotten. It has been the greatest experience of my working life being alongside Alex and a great honour to be able to call him a friend."
0902 GMT: AFP photographer Paul Ellis is at United's Carrington training ground south-west of Manchester: "Seven TV camera crews and four or five photographers outside the training ground.
"Players are expected to go to Chester Races this afternoon.
"Not clear if Ferguson is going too but he is believed to have two horses running there this afternoon."
WELCOME TO AFP'S LIVE REPORT on the news that Alex Ferguson will retire from Manchester United at the end of the season, bringing down the curtain on one of the most successful careers football has known.
Ferguson has been in charge at Old Trafford for 26 years, guiding United to 13 Premier League and two Champions League titles.
"The decision to retire is one that I have thought a great deal about and one that I have not taken lightly. It is the right time," Ferguson said in a statement released by the club.
"It was important to me to leave an organisation in the strongest possible shape and I believe I have done so," added Ferguson who will bow out with United having won this season's Premier League.
The club gave no indication of a successor amid press speculation that Everton's David Moyes could fill the Old Trafford hot seat vacated by fellow Scotsman Ferguson.
United did say, however, that Ferguson would remain at United as director and official club ambassador. His final game in charge will be against West Bromwich Albion on May 19.
Ferguson, who had recently insisted he would be continuing as manager, is due to have a hip replacement operation after the end of the season and until rumours started circulating Tuesday there was no indication he was about to step down.
Stay with us for all the breaking news and reaction.