Ten people have died and one remained trapped after the roof of a school gym collapsed in northeastern China, state media reported Monday.

The gym at the No. 34 Middle School in Qiqihar, Heilongjiang Province collapsed just before 3 pm (0700 GMT) on Sunday, state news agency Xinhua said.

As of 5:30 am Monday, 14 people had been pulled from the wreckage, state broadcaster CCTV said, “among whom four were pulled out without vital signs, and six died after treatment failed”.

Footage aired by CCTV showed the entire roof collapsed onto the gym and rescue workers picking through the debris.

“A search and rescue operation involving nearly 160 firefighters and 39 fire trucks has been launched,” CCTV said.

An initial investigation into the collapse found that construction workers had placed perlite — a form of volcanic glass — on the roof, Xinhua said.

Heavy rain then led the perlite to expand, causing the roof to collapse, it added.

“Those in charge of the construction company have been taken into police custody,” the state news agency reported.

Industrial accidents are common in China due to lax safety standards and poor enforcement.

One of the worst such accidents took place in 2015 in Tianjin, where a gigantic explosion at a chemical warehouse killed at least 165 people.