Firefighters investigate an explosion site at a school in Bangkok, Thailand on Friday, June 23, 2023.
CNN  — 

An 18-year-old boy was killed and dozens were injured when a fire extinguisher exploded during a drill at a high school in Bangkok on Friday, police and fire authorities said.

The extinguisher exploded during a fire drill at the Rajavinit Mathayom school, Thiti Saengsawang, commissioner of the city’s Metropolitan Police Bureau, told CNN. The cause of the explosion is being investigated.

Bangkok governor Chadchart Sittipunt said the fire extinguisher that exploded was a carbon dioxide-type model, according to Thai state news outlet National News Bureau of Thailand (NNT).

Bangkok’s Fire Rescue said 29 other people were injured by the explosion, mostly sustaining minor injuries.

Seven instructors at the school are being questioned by police in relation to the incident, state media reported.

The sound of the explosion could be heard in the nearby Government House, where the Thai prime minister and cabinet ministers have their offices, NNT reported.

Prime Minister Prayut Chan-o-cha has offered his condolences for the boy’s death, it added.