A miner is carried to the surface after an explosion in a coal mine in Yima, Central China's Henan province, Nov 4, 2011. The blast happened after a small earthquake near the mine on Thursday evening, which killed at least four miners.[Photo/Xinhua]

YIMA, Henan - Rescuers searching for survivors after a massive rock burst destroyed a mineshaft in Central China pulled seven workers to safety on Friday.

The men were returned to the surface above Qianqiu Coal Mine by late afternoon.

"Most of the injuries (they sustained) are bone fractures," said Zhao Liang, a medic with Yima Coal Mine Hospital, as he emerged after seven hours in the shaft.

Authorities handling the accident said on Friday that 50 more workers are still trapped underground.

The rock burst - a spontaneous, violent fracture of rock - occurred at about 7:45 pm on Thursday in a shaft roughly 10 km from downtown Yima, a city in Henan province.

The accident came just after a 2.9-magnitude earthquake, according to rescue headquarters, although it is not clear whether the tremor caused the blast.

There were 75 workers underground at the time. Fourteen managed to escape in time and four more were confirmed dead on Friday morning, officials said.

"I heard a bang and was knocked off my feet," recalled Peng Kechang, 45, one of the rescued miners at Yima Coal Mine Hospital on Friday night.

Peng has worked in the pit for more than two decades and was heading a safety team when the accident happened. Although pinned under a rock by one leg, he managed to find the blocked ventilation pipe and created a small opening by loosing two screws.

Without his bravery, rescuers said Peng and his six colleagues would most likely have suffocated.

The shaft is about 760-meter deep and the rock burst blocked off the shaft at the depth of about 480 meters, rescue headquarters said.

A spokesman for the State-run Yima Coal Group, which runs the mine, said the company has organized four rescue teams to operate in turns.

"Digging is going smoothly," said the leader of a 10-member rescue team, who declined to give his name. He said much of the coal has being cleared by hand.

"We have gone dozens of meters deeper since we reached the seven survivors at about 510 meters," he said.

Authorities say it is difficult to determine how deep the trapped workers are, and added that their chances of survival depend on the intensity of the explosion and the rescuers' ability to provide ventilation.

"If the impact caused the tunnel to collapse, the people trapped there may have suffocated," rescue headquarters said in a statement.

Yang Xiaonan and Liu Ce contributed to this story.

China Daily