A toxic gas leak from a chemical plant in east China's Zhejiang Province left five firemen ill and forced the evacuation of more than 2,000 residents late Friday.

On Saturday, one of the five firemen was still in intensive care in hospital after the incident in Hangzhou, the provincial capital, said a city government spokesman.

The other four firemen were still in hospital, but out of danger, he said.

At around 7 p.m. Friday, thick fumes were detected at a warehouse for toxic materials at a chemical plant of the Hangzhou Hexiang Fine Chemical Co., Ltd. in Xiangfu town.

Residents nearby began to smell a pungent odour, and their eyes watered and they complained of sore throats, said the spokesman.

At around 7:19 p.m., the fire brigade arrived at the scene and started to evacuate residents. They rescued 20 people from the factory area and evacuated 2,000 people.

Fire fighters used powder to stabilize the gas, and sprayed water to dilute it. In the early hours of Saturday, the situation was under control.

The five firemen developed symptoms of vomiting and dizziness and they were taken to hospital immediately.

The spokesperson said the toxic material was thiocarbamide. It emitted pungent gas in high temperatures.

Environment tests and monitoring are underway, and the cause of the accident is being investigated.