Twenty-three people were killed and one was rescued after an accident due to excessive levels of carbon monoxide in a coal mine in southwest China, rescuers said Saturday.

The accident happened at around 5 p.m. Friday at the closed Diaoshuidong colliery in Yongchuan District, Chongqing Municipality, when workers were dismantling equipment in the pit, trapping 24 workers underground. The mine was suspended and shut down over two months ago.

The cause of the accident is being further investigated.