Dozens of police and emergency responders gathered outside the cordoned-off Debsirin Nonthaburi School on Friday, Agence France-Presse journalists saw, while parents waited to pick up their children and tearful students and staff comforted each other outside.
Fifteen injured students were not struck by gunfire but hurt as they were trying to flee, deputy interior minister Polapee Suwunchwee told local broadcaster Thai PBS.
Police later said 23 people were injured.
The shooter was identified by local media as a teenage student of the school, and police said he died during the incident.
Some media reports said police officers had shot and killed him, while others said he had died by suicide.
‘Under stress’
“Police interrogated his close friend who said the suspect had been under stress” related to his schooling, Prime Minister Anutin Charnvirakul told reporters outside the secondary school in Nonthaburi province, bordering Bangkok.
Photos published by local media show the suspect wearing a purple school uniform and carrying a black cross-body bag, with several bullet casings visible on the ground.
An AFP journalist saw a dozen mental health workers arrive at the school, where traffic was nearly at a standstill.
Education Minister Prasert Jantararuangtong pledged to provide mental health assistance to students and ramp up security measures at educational institutions.
Thongchai Thanakat, a motorcycle-taxi driver who has worked in the area for 20 years, said he was waiting to pick up passengers outside the school when he heard more than 10 gunshots and saw a stream of students rushing out.
“Some of them weren’t even wearing shoes,” he told AFP.
“I feel very bad for one student whose body I saw after he was shot right through his head. It was very emotional for me.”