Eighteen miners were still trapped underground at a coal mine in northeast China after mud and rocks flooded into the shaft where they were working, state media reported on Tuesday.

The incident happened at around 2.30pm local time on Monday, stranding 25 miners in a shaft of the state-owned Zhenxing Coal Mine in Heilongjiang province.

Seven of the miners, who had been working near the shaft entrance, were rescued, CCTV reported.

The other 18 workers were excavating coal some 500 metres below the ground when the flow of mud and rocks poured in, it added.

The Zhenxing Coal Mine, established in December 1990, was designed to produce 600,000 tonnes of coal a year. An investigation into the cause of the incident is still underway.

China's mines are the deadliest in the world, due to lax enforcement of safety standards and a rush to feed demand from a robust economy.

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