Picture taken on Jan. 7, 2010 shows fire engines arriving at a factory in which an explosion occured in Lanzhou, capital of northwest China's Gansu Province. [Xinhua]

Six people are dead after a chemical plant blast in northwest China's Gansu Province, said company executives Friday.

"Six bodies were recovered from the scene," said Li Jiamin, deputy general manager of the Lanzhou Chemical Company of the China National Petroleum Corporation (CNPC).

One seriously injured person was in a critical condition, said Li.

Five with minor injuries were being treated in hospital. Nine more people were kept in hospital for observation. All of them are in Lanhua Hospital, Lanzhou.

The fire was under control, said Wang Xinjian, of Lanzhou Municipal Public Security Bureau.

The blast occurred Thursday afternoon at the plant run by the Lanzhou Chemical Company near the provincial capital of Lanzhou. The dead and injured were all CNPC employees.

An initial investigation showed a gas leak was the cause of the blast. Police are investigating the incident.

The plant was 30 km from downtown Lanzhou. Residential buildings near the plant were not affected, officials said.