At least 11 people were killed after a concrete roof collapsed on a number of people at a school gymnasium on Sunday, state media reported on Monday.

Six of those died after attempts to treat them failed, state broadcaster CCTV reported.

Around 15 people had initially been thought to have been trapped under the debris.

But authorities pulled around 14 individuals from the rubble, CCTV reported. Their ages are not known yet.

"A search and rescue operation involving nearly 160 firefighters and 39 fire trucks has been launched," the broadcaster said.

People in charge of construction company arrested

The deadly accident took place at the No. 34 Middle School in Longsha district in the northeastern city of Qiqihar.

The accident occurred at around 2:56 p.m. local time Sunday (0656 GMT), according to the provincial fire and rescue department, according to CCTV.

State-run news agency Xinhua said that construction workers had placed perlite — a form of volcanic glass — on the roof. An initial investigation found that heavy rain had caused the perlite to expand, thus bringing down the roof.

"Those in charge of the construction company have been taken into police custody," the broadcaster said.

There were reportedly 19 people at the gymnasium at the time of the accident, and four of them managed to escape.

An overhead aerial view of the scene from pictures on social media showed a completely collapsed roof with rescue workers in the gym next to large boulders of concrete.

Lax building safety standards are often the reason for such accidents in China which are not uncommon.

rm/ab (Reuters, AFP)