BEIJING (AP) — An explosion at a factory in China’s Inner Mongolia region killed two people and left 66 others hospitalized on Sunday.

China’s official news agency Xinhua said the blast, which sent heavy plumes of smoke into the sky, occurred at a plant of Baogang United Steel in the city of Baotou at around 3 p.m local time and caused tremors in the surrounding areas. The report also said three of those hospitalized suffered serious injuries, and five people remained missing.

Rescue crews rushed to the scene and authorities are still investigating the cause of the blast, the agency said.