More than 3,000 residents in an east China city were evacuated Saturday after tonnes of ammonia, a pungent industrial gas, leaked out from a factory, local officials said.

Ten people remain hospitalized in Leqing city, Zhejiang province, by 10 p.m. Saturday, nearly seven hours after the gas leak, officials said.

The factory boss said a valve was accidentally knocked off, causing the leak of about 1.4 tonnes of ammonia.

Doctors say inhalation of large amount of ammonia can cause lung hydropsy or even death in serious cases.