HOHHOT - An explosion went off Saturday in a residential building in north China's Inner Mongolia Autonomous Region, but casualties were not immediately known, local authorities said.

The accident happened at around 2 pm in a multi-storey residential building in Tumd Right Banner of Baotou City, causing part of the building to collapse, the local government said.

Investigators suspected the blast happened in the natural gas pipe but were yet to confirm the cause of the accident.