BEIJING — Eleven people have died after the roof of a school gymnasium in north-east China collapsed while it was being used by a girls' volleyball team, state media reports.

Many of the victims are children, eyewitnesses tell local media, although this is yet to be officially confirmed.

Anguished parents have thronged a nearby hospital seeking updates.

Only eight of the 19 people who were inside the gym in the industrial province of Heilongjiang survived.

A preliminary investigation found that perlite, a form of volcanic glass, had been illegally piled on the roof soaking up rainwater, which caused the collapse at 15:00 local time (07:00 GMT).

The coach of the middle school's girls' volleyball team was heard calling out the students' names as rescue teams clawed through the rubble in Qiqihar city, China National Radio reported.

Parents questioned school officials, saying there had been a lack of proper communication on the rescue effort, which stretched until Monday morning.

"They tell me my daughter is gone but we never got to see the child. All the children had their faces covered with mud and blood when they were sent to the hospital. I pleaded, please let me identify the child. What if, that wasn't my child?" one man said in a video that has been widely shared on social media.

"What have [the authorities] been doing four, five, or even six hours after the children were sent to hospital? ... Doctors are not communicating with us about how the rescue is going," he said.

"We have elderly people at home, we need to [help them] be mentally prepared. There are doctors, police officers and other government officials here. But we have not heard anything from you," he said.

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

In June, an explosion at a barbecue restaurant in north-west China killed at least 31 people. A preliminary investigation found that a restaurant employee was replacing a broken valve on a liquefied gas tank when the blast occurred.

In April, a fire at a Beijing hospital killed 29 and led some desperate survivors to flee by jumping out of the windows. — BBC