An explosion at a coal mine in northern China has killed at least 21 miners, according to reports in Chinese state media.

The accident happened in the Wuju coal mine, close to Datong city in Shanxi province on Saturday.

The area is one of China's prime coal producing areas.

Four miners were rescued by emergency workers, Xinhua News Agency said, while seven others managed to escape on their own.

The cause of the explosion is not known.

All of the victims died of carbon monoxide poisoning, Xinhua reported, citing an unidentified city official.

China's mines are among the most dangerous in the world, with safety standards often ignored in the quest for profits and the drive to meet a soaring demand for coal - the source of about 70 per cent of China's energy.

Nearly 3,800 lives were lost in Chinese mines last year from explosions, cave-ins and floods, down 20 per cent from the year before, according to official figures.