An accident at a coal mine in the southwest has killed 21 miners, in the latest disaster to hit the mainland's troubled industry.

Four others were missing after the coal and gas blast at the Machang coal mine in Guizhou, Xinhua reported, citing local authorities. The agency added that 58 more people had managed to get to the surface safely.

The mainland's mines are among the deadliest in the world due to lax regulation, corruption and inefficiency. Safety is often neglected in the pursuit of profit. Official figures show 1,973 people died in coal mining accidents on the mainland in 2011, a 19 per cent fall on the previous year.

Labour rights groups, however, say the actual death toll is likely to be much higher, partly due to under-reporting of accidents as mine bosses seek to limit their economic losses and avoid punishment.

The mainland is the world's biggest consumer of coal, relying on the fossil fuel for 70 per cent of its growing energy needs.