Sixteen people were injured after an explosion shocked a factory in the city of Wenzhou in Zhejiang province on Sunday, local authorities said.

The powerful explosion happened at around 1:28 pm in the city's Lucheng district, razing the upper floor of a two-story polishing factory and leaving the site in heavy smoke, said one rescuer.

Sixteen people, who were mostly workers from the factory, were injured, and five were reported in serious conditions. Firefighters also evacuated more than 100 nearby residents.

The cause of the accident is under investigation.