GUIYANG - Five people were injured and about 20,000 were evacuated after a chemical plant blast in Southwest China's Guizhou province on Monday morning, local authorities have said.

The accident happened at about 10:20 am at a factory of Bestchem Co Ltd in the provincial capital city of Guiyang, a municipal government official said at the site.

Firefighters are still working there, with heavy smoke filling the sky.

About 20,000 people within a 1.5-km vicinity of the factory have been evacuated to safe places, the official said.

The factory, located in Baiyun District of Guiyang, mainly produces pyrethroid.

The cause of the accident is under investigation.