HOHHOT: A total of 202 people fell ill Wednesday after an ammonia gas leak at a pharmaceutical plant in north China's Inner Mongolia Autonomous Region, the local government said.

Poisoned people receive treatment in a local hospital in Chifeng City of north China's Inner Mongolia Autonomous Region, August 5, 2009. [Xinhua]

The government of Hongshan District, Chifeng City, said Wednesday afternoon 21 people were hospitalized and the 181 others remained under hospital observation. No one died in the leak.

The leak occurred at 8:40 am when a truck carrying 30 tonnes of liquid ammonia was unloading at the factory of Chifeng Pharmaceutical Group, but was sealed in about 50 minutes, the government said.

A pipe suddenly burst during the unloading, according to the government.

The 202 people are workers in the factory, emergency rescuers and  residents living nearby.

People within 2 km downwind of the leak were evacuated.

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.

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

Fire fighters cool the site where an ammonia gas leak occurred at Chifeng Pharmaceutical Factory in Chifeng City, north China's Inner Mongolia Autonomous Region, Aug. 5, 2009. [Xinhua]

A fire fighter walks at the site where an ammonia gas leak occurred at Chifeng Pharmaceutical Factory in Chifeng City, north China's Inner Mongolia Autonomous Region, Aug. 5, 2009. [Xinhua]