China's coal mines are the deadliest in the world with 7,000 fatalities in 2002 [Reuters]

Seven miners have been pulled to the surface and rescuers are trying to reach 50 more trapped in the Qianqiu coal mine in Sanmenxia in Henan province, central China, after a rock explosion.

CCTV, the state broadcaster, showed rescuers with helmets and oxygen tanks carrying out the seven survivors, early on Friday afternoon, from a mine elevator.

Xinhua news agency reported that one of the rescued miners was seriously hurt, while the six others had sustained minor injuries.

A small earthquake near the mine caused the rock blast on Thursday evening.

Four miners were killed in the explosion, while 14 managed to escape the blast.

The tunnel within which the miners were working had “basically folded'' a little more than halfway down the passage, at 480 metres, reported Xinhua.

Structural status

At least 200 workers were digging a small rescue tunnel of about 760 metres long in an attempt to reach the trapped miners, but it was unclear what the condition of the tunnel was beyond that point of the collapse.

The structural status of the mine and the conditions of the trapped miners were not known.

The survival of the miners depends on the intensity of the rock explosion and the rescuers' ability to provide ventilation to them, a local official told the AP news agency.

"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," said an official from Yima city Communist Party's, who would give only his surname, Tian, as is common with Chinese officials.

"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.

He said it was difficult to determine how deep in the mine the trapped workers were.

Lethal explosions

The exploding chunks of coal and rock, or the shock waves, can be lethal.

Luo Lin, the head of the work safety department at the State Administration of Work Safety, said a magnitude 2.9 earthquake occurred near the mine shortly before the "rock burst" was reported.

The phenomenon occurs when settling earth bears down on mine walls and causes a sudden, catastrophic release of stored energy.

China's coal mines are the deadliest in the world, although the industry's safety record has improved in recent years as many smaller, illegal mines have been closed.

Annual fatalities are now about one-third of the high of nearly 7,000 in 2002.

Last Sunday, a gas explosion at a coal mine in central China's Hunan province killed 29 workers, the worst accident in recent months.

The Qianqiu coal mine belongs to Yima Coal Group, a large state-owned coal company in Henan, the State Administration of Work Safety said on its website.

Source: Al Jazeera