An explosion at a fireworks plant in northern China has killed 15 people and injured six others, state media reported Sunday.

The blast occurred Saturday at the Xinxin Fireworks Plant in Inner Mongolia, the official Xinhua News Agency reported.

Xinhua cited a regional work safety official as saying Sunday that the explosion also destroyed about 50 workshops.

A preliminary investigation found the blast occurred when workers were weighing and mixing ingredients for fireworks, the agency said.

Accidents in Chinese factories are common, with thousands dying every year in part because of lax enforcement of safety rules. Fireworks factories, many of them illegal, are notoriously unsafe.