Rescue workers prepare to go underground to search for miners trapped in Qianqiu Coal Mine in Yima, Henan province, Nov 4, 2011. [Photo/Xinhua]

SANMENXIA, Henan - Rescuers are lifting seven injured miners to the surface from a coal mine in central China's Henan province after a rock burst Thursday killed four and trapped another 50, local rescue headquarters said Friday.

Six of them had sustained minor injuries, and the other one had been seriously injured when rescuers located them 510 meters underground Friday morning. They will be rushed to hospital as soon as they reach the ground, the rescue headquarters said.

The accident happened at around 7:45 pm in the Qianqiu Coal Mine in the city of Sanmenxia, the Henan Administration of Work Safety said in a statement.

A total of 75 miners were working in the shaft at the time of the accident, of whom 14 managed to escape, the administration said.

The shaft is about 760-meters deep and the rock burst blocked off the shaft at a depth of about 480 meters, which has hampered ongoing rescue efforts, according to the rescue headquarters.

A 2.9-magnitude earthquake hit the city of Sanmenxia at about 7:18 pm Thursday, and the rock burst was later reported from the shaft in the Qianqiu Coal Mine, according to the rescue headquarters.

The coal mine, with an annual production capacity of 2.1 million tonnes, belongs to Yima Coal Group, a major state-owned coal enterprise in Henan.

Rescue workers prepare to go underground to search for miners trapped in Qianqiu Coal Mine in Yima, Henan province, Nov 4, 2011. [Photo/Xinhua]

Rescue workers unload a truck in the rain in Yima, Henan province, Nov 4, 2011, after a rock burst at Qianqiu Coal Mine killed four miners and trapped 57 others. [Photo/Xinhua]