Rescuers in China were battling against the clock on Friday to rescue 50 coal miners trapped underground after a sudden explosion of rocks killed four of their colleagues.

An official at the state-owned company that owns the colliery in Henan province told AFP rescuers had detected signs of life from the workers nearly 24 hours after the accident occurred.

A rock burst -- involving a violent explosion caused by massive pressure -- occurred in the mine shaft on Thursday evening, trapping the miners, according to the official Xinhua news agency.

A spokesman for the Henan Yima Coal Mine Group that owns the colliery, who refused to be named, said four workers had been confirmed dead and 57 were trapped in the mine shaft.

Another company official, who gave his surname as Du, later told AFP seven of the workers had since been rescued.

"The location of the other miners has been confirmed and we are stepping up rescue efforts," he said, adding the rescuers were currently 200 metres (660 feet) away from the trapped workers.

"We can still detect signs of life from the trapped miners."

Six of those rescued had sustained minor injuries while the seventh was seriously hurt, Xinhua said. Du said all seven were in a stable condition.

State television showed images of the rescued miners being pulled out of the shaft one after the other to huge applause, lying on stretchers covered by blankets as nurses rushed to look after them.

The images were reminiscent of those broadcast round the world from Chile in October last year, when 33 workers trapped underground for 69 days in a mine in the Atacama Desert were pulled out in a dramatic 22-hour rescue.

The rock burst in Henan happened moments after a 2.9 magnitude earthquake shook Sanmenxia city, where the mine is located, Xinhua said. It was not immediately clear whether the earthquake directly caused the accident.

The incident is the latest to hit the hazardous mining industry in China, and came days after a gas explosion in a state-owned coal mine in neighbouring Hunan province left 29 miners dead.

Earlier in October, blasts in the southwestern city of Chongqing and the northern province of Shaanxi killed 13 and 11 miners respectively.

In 2010, 2,433 people died in coal mining accidents in China, according to official statistics -- a rate of more than six workers per day. Campaigners suggest the true figure is likely to be far higher.

China's rapid economic growth has caused demand for energy, including coal, to surge. Critics say some mining bosses have put the safety of workers at risk to chase profits.