The blast occurred at 7:29 pm (1129 GMT) on Friday at the Liushenyu coal mine in Shanxi province, according to state news agency Xinhua.

A total of 247 workers were underground at the time, of whom 201 had been brought to the surface safely as of 6:00 am on Saturday, Xinhua said.

Eight people have been confirmed dead, while 38 remain trapped underground, the agency reported, citing local emergency management authorities.

Rescue efforts were continuing, and "the cause of the accident is under further investigation", Xinhua said.

It reported earlier that levels of carbon monoxide -- a highly toxic, odourless gas -- had "exceeded limits" at the mine.

Some of those trapped underground were in "critical condition", the earlier report said.

Shanxi, one of China's poorer provinces, is the country's coal-mining capital.

Mine safety in the country has improved in recent decades, but accidents still occur frequently in an industry where safety protocols are often lax.

China is the world's top consumer of coal and the largest greenhouse gas emitter, despite installing renewable energy capacity at record speed.