LANZHOU - Four people were dead and another ten were injured after a carbon monoxide poisoning occurred at a chemical plant in Northwest China's Gansu province on Sunday night, local authorities said Monday.

The accident happened at about 11 pm at a sodium sulfide manufacturing workshop at Gansu Jinshi Chemical Co Ltd, which is based in Minle county, according to the provincial work safety administration.

Four died at the scene. Ten are receiving treatment at local hospitals, of whom four are receiving intensive care, according to the bureau.

The cause of the accident is under investigation.