Rescuers are trying to reach 50 miners trapped after a cave-in at a coal pit in central China, official say.

Seven injured miners were pulled to the surface today.

Four miners were killed when the cave-in blasted rock into the mine shaft on Thursday and 14 managed to escape, the official Xinhua News Agency said.

The rock explosion happened just after a small earthquake near the mine in the city of Sanmenxia in Henan province.

State broadcaster CCTV showed rescuers with helmets and oxygen tanks carrying the seven found alive from a mine lift as waiting officials applauded and medical staff rushed to attend to them.

The rescued miners lay on stretchers, wrapped with blankets with their eyes covered by towels to prevent them from being damaged by the sudden exposure to light after hours of being trapped.

Six had minor injuries.

At least 200 workers were digging a small rescue tunnel about 1,650 feet (500 metres) deep to try to reach the trapped miners.

There have been no reports of communication with the trapped miners.

The mine belongs to Yima Coal Group, a large state-owned coal company in Henan.

Luo Lin, head of the state work safety body, said a magnitude-2.9 earthquake occurred near the mine shortly before a "rock burst" was reported.

This happens when settling earth bears down on mine walls and causes a sudden release of stored energy. The exploding chunks of coal and rock, or the shock waves alone, can be lethal.

China's coal mines are the deadliest in the world, although the industry's safety record has improved in recent years as 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.