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. A tank truck spilled ammonia while transmitting liquid ammonia into the workshop in the Chifeng Pharmacy Plant on Wednesday, with over 30 people poisoned as local source reported. Local rescue departments have blocked the leakage and evacuated personnel in 2 kilometers leeward of the venue. [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 a.m. 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 responders 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 old pipes.