A total of 21 Chinese coal miners were killed after a shaft they were working in flooded with water, an official told AFP Thursday, the latest incident in the loosely-regulated industry.

Water from a "ground-level reservoir" flooded the mine in Datong in the northern province of Shanxi, where 247 people were working, the official Xinhua news agency said, citing China's work safety regulator.

"The final figure is 21 dead, three rescued," an official surnamed Li from the Shanxi Administration of Coal Mine Safety said.

"The cause of the flood is still under investigation," she told AFP.

Xinhua said 223 miners at the Jiangjiawan Mine "made it out safely", while 24 were trapped. Four miners were pulled out alive by rescuers after the accident Sunday, but one of them later died in hospital, it added.

The mine is owned by Datong Coal Mine Group and has an annual production capacity of 900,000 tonnes, the news agency said.

Accidents in Chinese coal mines killed 931 people last year, a top work safety official said last month.

The number of mining fatalities continues to decline in China, the world's largest producer of coal, but some rights groups argue the actual figures are significantly higher due to under-reporting.

Last November, 11 people died in a coal mine explosion in the southwestern province of Guizhou.

That accident came a day after a fire at a mine in Liaoning province in the northeast that killed 26 people.