GUIYANG -?Four workers were killed and another was injured when a highway tunnel under construction collapsed in Southwest China's Guizhou province on Wednesday morning, local authorities said.

The accident happened at about 8 am at the Bianyang Tunnel on the Huishui-Luodian Highway, according to the Luodian county government.

The injured worker is receiving treatment at a local hospital.

The cause of the accident is being investigated.