More than 100 people fell ill Wednesday after an ammonia gas leak at a pharmaceutical plant in north China's Inner Mongolia Autonomous Region, local police said.

The leak occurred at 9:40 a.m. when a truck carrying 50 to 60 tonnes of liquid ammonia was unloading at the workshop of Chifeng Pharmaceutical Factory in Chifeng City, said Wang Suoyou, commissar of the fire control detachment of the city's public security authorities.

The leak had been sealed, Wang said.

Local public security, environment protection and work safety authorities had set up a team to investigate the accident. Authorities were also testing the city's water supplies for ammonia contamination.

About 300 police officers were maintaining order on the site.

An initial investigation suggested that the leak was caused by workers failing to operate the equipment properly and old pipes.

People within 2 km downwind of the leak were evacuated.

(Xinhua News Agency August 5, 2009)