HOHHOT, July 31 (Xinhua) -- A tunnel under construction collapsed early Friday in Ulanqab City, north China's Inner Mongolia Autonomous Region, leaving four people dead and six others injured, according to local authorities.

The accident happened at around 3:50 a.m. at the tunnel construction section undertaken by the China Railway 15th Bureau Group Co., Ltd. for Zhuozi County, Ulanqab.

The search and rescue operation is continuing. Treatment for the injured and accident investigation are currently underway.