The victims were poisoned by carbon monoxide which may have started from a gas blast or a spontaneous ignition, according to a local government official.
Seven miners managed to escape and rescuers helped four people out of the mine but the official number of miners underground at the time of the accident was still unknown, China’s state news agency Xinhua reported.
A rescue operation is still underway.
The accident took place on Saturday morning at the Wujiu Coal Mine in China’s northern city of Datong.