An explosion at a coal mine in Henan, China has killed four people and trapped 57 miners underground.

Rescuers have pulled seven people out of the Qianqiu shaft in the city of Sanmenxia in the central Chinese province of Henan on Friday, but 50 more are still trapped.

The rock explosion occurred on Thursday night, after a small 2.9 magnitude earthquake shook the region, according to The Associate Press. Around 200 rescue workers are digging a tunnel to reached the miners, who are trapped 1,650 feet underground.

Authorities do not know the severity of the original blast, and the miners' survival depends on how quickly rescuers can get to ventilate the space where the workers are trapped.

If it was not very strong, it might have caused the tunnel to get narrower, but we might still be able to send some air in there to ensure ventilation, Yima city Communist Party's head of propaganda, who would give only his surname, Tian, told the AP.

But if the impact was pretty strong and caused the tunnel walls to collapse, then the ventilation was probably cut off immediately, suffocating the people trapped there, Tian said.