At least 21 miners have died after a coal mine accident in north China's Shanxi Province on Saturday morning, local authority said on Sunday.

All the victims had been poisoned by carbon monoxide at around 11:20 a.m. at Wujiu Coal Mine in Nanjiao District, Datong City, said a Datong city government official.

Seven miners managed to escape on their own and four were helped out, the official said.

The number of miners who were working underground at the time was still unknown and rescuers had launched a search, the official said.

Preliminary investigations showed a gas blast or spontaneous ignition were the likely causes of the gas.

The coal mine was registered with an annual production capacity of 150,000 tons.

Datong, in the north of the coal-rich province, has been called China's "capital of coal".

(Xinhua News Agency July 7, 2008)