TAIYUAN -- Four people have been confirmed dead, and 90 remain trapped underground after carbon monoxide levels exceeded limits in a coal mine in Changzhi city, North China's Shanxi province, on Friday night.

The accident happened at 9:43 pm on Friday in the Liushenyu coal mine in Qinyuan County of Changzhi, where a total of 247 workers were underground at the time.

By 3:33 am on Saturday, 157 people had been brought to the surface, including four people confirmed dead. A total of 90 people remained underground, 16 of whom were in critical condition.

Intensive rescue efforts are ongoing.