Twenty miners were killed in the explosion on Monday in the state-owned Xingergou mine near the city of Datong and 13 others died later in hospitals, the official Xinhua News Agency said.

Some 286 mine workers were rescued after the explosion, Zhao Tiechui, deputy director of the State Administration for Work Safety, was quoted as saying Monday by state television.

The cause of the explosion is under investigation.

Chinese coal mines have the worst safety record in the world. Official figures indicate more than 5,000 people were killed last year alone, while other estimates suggest the figure could be much higher.

Such explosions are usually caused by the accidental ignition of gas that seeps from the coal and builds up due to poor ventilation.

Many such incidents occur in privately owned mines, which lack operating licences and adequate safety equipment.

China relies heavily on the coal industry for its energy needs.