BEIJING - DOZENS of rescuers were battling through thick coal dust late on Saturday in a bid to reach 16 miners trapped underground after a coal mine accident killed 21 of their colleagues, Chinese state media reported.

The mine in the central province of Henan was hit by a 'sudden coal and gas outburst' as 276 miners were at work below ground, the national work safety agency said on its website, confirming the toll.

It is the latest tragedy to highlight appalling safety conditions in the nation's mines, in which over 2,600 miners perished last year according to official figures.

A total of 239 miners made it to the surface following the accident in the city of Yuzhou, but 21 others have been found dead and 16 remain missing, the Xinhua report said.

Rescuers said they had located the missing miners around 50 to 80 metres below the pit entrance but their progress through the narrow tunnels was slowed by the heavy dust. The condition of the trapped miners was unknown.

'The thick dust in the shaft is hampering the rescue. We must clear the dust first,' an engineer called Du Bo was quoted by Xinhua as saying. He said more than 2,500 tonnes of coal dust had smothered the pit after the gas leak, suffocating most of the victims. Officials said work crews are struggling to retrieve the victims' remains from the mine.

China mine accident kills 21