A suspected toxic gas leak near a detention facility in southwest China Monday caused the poisoning of nine inmates, witnesses and local officials said Tuesday.

Inmates of the Xishan Detention Center in suburban Kunming City, Yunnan Province, said they smelt a pungent gas Monday night, a district government spokesman told reporters Tuesday.

Some inmates suffered headaches and nausea, and some had difficulty breathing. The nine poisoned inmates - three males, six females - were taken to hospital.

The pungent gas had dispersed by late Monday night.

Work safety officials are checking factories located near the detention for gas leaks.