At least 11 people are now known to have died after the roof of school gymnasium collapsed under heavy rain in north-east China, state media reports.

Officials say 19 people were trapped inside the gym when it collapsed.

Eyewitnesses told media that many of the victims are children, although this is yet to be officially confirmed.

Police have arrested the person in charge of the building in Qiqihar city in the industrial Heilongjiang province.

Officials say four people managed to escape. Of the 15 people pulled out of the rubble, only four have survived.

Perlite, a form of volcanic glass, that was piled on the roof soaked up rain water, causing it to collapse at 15:00 local time Sunday, investigators say.

Construction accidents are common in China and have been blamed on lax safety standards and poor enforcement. (BBC)