HARBIN -- Eleven people were confirmed dead after the roof of a school gymnasium collapsed Sunday in Qiqihar city, Northeast China's Heilongjiang province.

The roof collapse was reported at 2:56 pm Sunday, according to the provincial fire and rescue department.

There were 19 people at the gymnasium covering about 1,200 square meters at the No 34 Middle School in Longsha District when the accident occured. Four people escaped on their own and 15 were trapped, the municipal search and rescue headquarters said.

As of 10 am Monday, the last trapped student was pulled out without vital signs. 

Preliminary investigation found that construction workers illegally placed perlite on the roof of the gymnasium during their construction of a teaching building adjacent to the gymnasium. Under the influence of rainfall, the perlite soaked in water and gained weight, resulting in the roof collapse.

The gymnasium's walls have a grid structure, and the roof is made of concrete slabs, according to local authorities.

An in-depth investigation is ongoing. Those in charge of the construction company have been taken into police custody.