NANNING - Five people have died and two others were injured after being poisoned by carbon monoxide at an unlicensed fish processing mill in south China's Guangxi Zhuang autonomous region, local authorities said Wednesday.

Three workers at the mill in the city of Beihai accidentally fell into a pool of salted fish at 4 p.m. and fainted after inhaling carbon monoxide generated during the fermentation process, according to rescuers.

The owner of the mill, his father and two sons tried to rescue the workers but were affected by the poisonous gas in the pool.

The owner, one of his sons, his father and two workers were found dead after a rescue team arrived around 4:30 p.m. The owner's other son and a worker survived after they were rushed to hospital.

There was no protection around the pool when seven workers were trying to take out the salted fish. The owner runs the mill without a license issued by local authorities, rescuers said.

An investigation is underway.