An explosion and fire Monday morning at a chemical plant in southwestern China injured at least five workers and forced the evacuation of more than 20,000 people in the area, RT News reported.

Firefighters battled the blaze for several hours as a dark cloud of smoke was seen rising from the plant. The five injured employes were rushed to local hospitals for treatment. Evacuees included students and teachers from a nearby college.

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There has been no official announcement regarding the cause of the explosion, but the initial investigation revealed that leakage and burning of materials contributed to the blast, according to RT News.

Located in the Chinese province of Guizhou, the Bestchem plant produces pyrethroids, which are used in the production of insecticides and insect repellents.