HANGZHOU - Toxic gas given off by chemicals stockpiled amid the SARS scare nine years ago forced more than 800 workers to evacuate an office building in downtown Hangzhou, capital of East China's Zhejiang province, on Friday.

White smog with a suffocating odor fumigated the 19th floor of Tianyuan Mansion in Hangzhou's Xihu district at 7:30 am, according to a spokesman with the local fire brigade.

He said the office building, which accommodates about 1,500 people during working hours, was half empty at the time. "But the smog caused panic among the early birds, who rushed downstairs and called emergency services."

The firefighters traced the smog to a warehouse where about 3 kg of chlorine dioxide powder was stored.

Management of the building said the chemical was used as disinfectant during the SARS epidemic in 2003 and the leftover had not been disposed of.

The firefighters removed the chemical from the building and launched a cleanup.

Investigators from the local environment protection and work safety authorities tested the indoor air quality before declaring the office building safe.