At least ten people are dead and one still trapped following the collapse of a middle school gymnasium roof in China's northeastern city of Qiqihar Sunday afternoon, Chinese state media CCTV reported.

Nineteen people were at the gymnasium when the accident happened. Four escaped and fifteen were trapped at the time, according to the municipal search and rescue headquarters.

Rescue efforts are still underway.

A preliminary investigation suggests the collapse may have been caused by misplaced construction material called perlite that was left on the gym roof during construction work on an adjacent building.

The material gained weight after being soaked in water brought by rainfall and led to the collapse, according to the preliminary investigation.

Those in charge of the construction are being held in police custody. Authorities say they are conducting further investigations into the case.

Safety incidents are not uncommon in China and the accident follows a string of tragedies that have been linked to lax safety standards in recent months.

Last month, an explosion at a barbecue restaurant in northwestern China left 31 dead and prompted official pledges of a nationwide campaign to promote workplace safety, with Chinese leader Xi Jinping calling on all regions to "screen for and rectify all types of risks and hidden dangers."

That accident followed a coal mine collapse in Inner Mongolia in February that left 53 dead, while in April, the deadliest fire to hit Beijing in two decades killed 29 people in a hospital.