Two rival groups of teenagers clashed on Monday night at a charity concert featuring music legends Ad Carabao and Sek Loso, forcing an abrupt and early end to the show, police said.
The "Light of Hope" concert was at the Port Authority of Thailand Stadium in Bangkok's Klong Toey district.
Police said the fight started around 10pm when a group of about 50 vocational students exchanged words with another group of local Klong Toey youths.
The scene turned chaotic after the crowd heard what sounded like gunshots or firecrackers, causing concert goers to run off in all directions.
The concert was forced to end early, just as Ad Carabao started performing his third song, following Sek Loso's performance.
A team of 700 police officers were deployed to stop the riot and used tear gas on the brawling mob. Calm was not restored until about 1am.
Police detained about 50 rioters - many of them teenagers. They were later picked up by their parents at the police station.
Four people were injured. Two of them sustained tear gas injuries.
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Thirapat Sornpakdee, who was at the concert, said that Ad Carabao was asking the unruly crowd through his microphone to treat each other like brothers and sisters before begining his third song, but the mob remained rowdy.
"I ask the youths not to fight each other. I was a teenager once and I've been there before but the artists want to perform for us," Mr Thirapat said.
Thanuwat Meewan, a photographer at the event, said there was no problem with the Sek Loso's show.
He said the situation became more intense after Ad Carabao finished performing his second song. The third song "Yai Ku Za (My Grandma's a Hipster)" is not that arousing to cause a fight, he added.
"Some of the people who were at the show were 50 to 70 years old and these educated teenagers should have behaved well," Mr Thanuwat said.
Chaiyuth Limlawan, one of the event organisers, said there were 300 staff overseeing security inside the stadium and 400 others outside.
"When the incident began, Ad Carabao and our team spent about 30 minutes assessing the situation and agreed if we carried on with the show then someone might have died.
"We then decided to play the royal anthem to prevent the situation geting worse," Mr Chaiyuth said. This brought the show to a sudden end, but the rioting continued.
Last week, a fatal shooting occurred at a music festival in Khao Yai, Nakhon Ratchasima province. A 45-year-old man was shot in the heart by a drunken man after they had a small argument. A woman also sustained a gunshot wound to the leg.
In December last year, two rival groups of teenagers traded blows and threw beer bottles at each other at Pongsit "Pu" Kampee concert. The concert ended prematurely, as the Song for Life singer pleaded the rioters to stop fighting because there were women and children at the show.
The video clips of the riot at the charity concert was uploaded to YouTube by superent02 on Jan 15, 2013.