JINAN - An explosion ripped through a residential building in the coastal city of Weihai in East China's Shandong province early Monday morning, causing an unknown number of casualties.

The blast hit the building's fifth floor at around 1 am and subsequently caused a fire. Other floors also suffered damages, witnesses said.

Preliminary investigation indicated the blast was caused by a gas leak. Authorities are conducting a rescue and verifying the exact number of casualties.