Twelve people died when a gas pocket ignited in a coal mine in north China's Shanxi Province, local officials said Monday.

The accident occurred at 11:30 PM Sunday when 16 miners were working in a shaft in the Donggou Colliery in Jiexiu City, said a spokesman with the Shanxi Provincial Work Safety Administration.

The mine was expanding its annual production capacity from the authorized 30 tonnes. The workers violated a safety rule that prohibited the demolition of a wall between the shaft and a disused area of the mine where the gas was accumulated in high density, the spokesman said.

The four survivors were under observation in hospital. Their conditions were unavailable.

(Xinhua News Agency December 28, 2009)