A gas blast at a coal mine in China killed 21 miners Tuesday, with four others still missing, state media reported.

The official Xinhua news agency said 83 miners were working underground at the Machang Coal Mine, in Guizhou province, when the blast happened on Tuesday evening and 58 people of them managed to get to the surface safely.

The incident comes as the latest blow to hit the country’s crumbling industry, plagued by lax regulations, corruption and inefficiency.

China’s mines are among the world’s deadliest, with corrupt authorities compromising safety in order to chase quick profits.

According to official figures, nearly 2,000 people died in coal mining accidents in China in 2011, a 19% drop from the previous year.

Labour rights groups say under-reporting by mining authorities has put the figures much lower than the actual death toll, AFP reports.

China is the world’s biggest consumer of coal, relying on the fossil fuel for 70% of its growing energy needs, driven by rapid economic growth.