Hungarian Foreign and Trade Minister Peter Szijjarto tested positive for Covid-19 after arriving in Bangkok on Tuesday and was to return home by private plane on Wednesday.
Public Health Minister Anutin Charnveerakul said on Wednesday that Mr Szijjarto was being treated in isolation at ฺBamrasnaradura Infectious Diseases Institute.
Two aircraft had been sent by the Hungarian government to take him and his accompanying delegation back to Budapest. They would depart later on Wednesday.
Mr Szijjarto arrived in Bangkok on Tuesday for a two-day visit as a guest of the Foreign Ministry. The delegation arrived at 6.30pm. All were tested for the coronavirus at 9pm.
The tests, conducted at two labs, confirmed the minister was infected with the virus, although he showed no symptoms. The 12 officials accompanying him were negative, Mr Anutin said.
The minister would return to Hungary on one plane, and his delegation on the other.
Mr Szijjart's schedule had included a call on Prime Minister Prayut Chan-o-cha at Government House on Wednesday. All activities were cancelled after he was found to be infected.
Gen Prayut said the government would treat him until he left the kingdom.
Mr Szijjarto flew into Phnom Penh Tuesday for a one-day official visit to sign agreements on civil aviation, agriculture and water management, as well as reopening an embassy after a 25-year hiatus.
During his Cambodia visit, Szijjarto was pictured with Hun Sen at a meeting where neither appeared to be socially distancing or wearing a mask.
He also met his Cambodian counterpart and shook hands with a coterie of other ministers.
All of those people would now be tested and quarantined, according to Phnom Penh's Foreign Ministry.
Hun Sen announced on his official Facebook page Wednesday night that he was in the clear.
"I and my wife, my 18 bodyguards, and drivers have tested negative... but doctors require me to be in quarantine for 14 days," he said, adding that he will continue his duties as normal.
"I still can exercise and play golf inside my home compound, but I won't let others come close."