Eleven people have died after the roof of a school gym collapsed in northeastern China, mainland media reported on Monday.

The gym at the No. 34 Middle School in Qiqihar, Heilongjiang Province collapsed just before 3 pm on Sunday, Xinhua said.

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. (AFP)