Eight of them need treatment for poisoning and the rest are under observation, the provincial administration for workplace safety supervision said on Saturday.

The accident happened at 10:40 p.m. at Xinyu Chemical Co. Ltd, a new plant that was inaugurated only on Thursday in the industrial city of Panzhihua. The leak was capped overnight and caused no evacuation.

nvestigators have blamed the accident on equipment failure.

Huang Yanrong, vice governor of Sichuan, has demanded 24-hour monitoring of the local air quality.

Located in the hilly Sichuan province 2,100 kilometers southwest of Beijing, Panzhihua is home to one of China's largest steel makers and many mines and small factories.