Media playback is unsupported on your device Media caption The BBC's Michael Bristow: "Rescuers are continuing to look for miners"

Dozens of miners have been trapped in a coal mine in China after a "rock burst", officials say.

Four miners were killed and 50 more are missing after the accident, which happened late on Thursday in the city of Sanmenxia in Henan province.

State media reported that the rock burst - an explosion caused by the sudden release of built-up pressure - happened shortly after an earthquake.

Hundreds of Chinese miners die every year in pit accidents.

The industry is one of the most dangerous in the world, and is notorious for its lax safety standards.

Earlier this week a gas explosion at a mine in neighbouring Hunan province killed 29 people.

But officials insist the country's record is improving, and say they have taken action by closing many illegal mines.

'Location confirmed'

State TV showed images of seven miners being carried out of the pit alive by rescue teams carrying oxygen tanks.

Six were said to have sustained minor injuries while one was seriously hurt.

Officials from the state-run Yima Coal Group, which runs the Sanmenxia mine, said an "intense search" was going on for the missing miners.

"The location of the other miners has been confirmed and we are stepping up our rescue efforts," a company spokesman told the AFP news agency.

Local safety officials said 75 miners had been working in the pit at the time of the explosion.

They were reportedly in a 760-metre-deep shaft which was blocked by the rock burst at a depth of 480 metres.

Some 14 managed to escape, seven were rescued and four have been confirmed killed, leaving 50 others trapped.

An earthquake with a magnitude of 2.9 hit the area shortly before the rock burst.

Government safety chief Luo Lin told state-run CCTV that the tremor had helped to cause the rock burst.