HARBIN -- Four miners have been rescued and the remaining four were still trapped in the flooded coal pit in Northeast China's Heilongjiang Province by 6 p.m. on Wednesday, said rescue headquarters.

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The flooding occurred at 6:40 p.m. on Tuesday at Fusheng Coal Mine in Boli County, Qitaihe city when nine miners were working underground.

Only one miner managed to get out of the flooded pit himself, said rescue officials.

Rescue work is underway and the cause of the flooding is being investigated.

The privately-run Fusheng Coal Mine has a designed production capacity of 60,000 tons a year.

In a separate incident, 12 miners were killed in a colliery explosion which was thought to be caused by illegal use of explosives early Wednesday morning in Hengyang, a city in central Hunan province.

China's coal mines suffered frequent flooding, explosions and cave-ins, killing around 6,000 people a year.