Two mine managers died of asphyxiation in a copper mine in south China's Guangxi Zhuang Autonomous Region Wednesday, authorities said Thursday.

Three mine managers - surnamed Bi, He and Pan - were 800 meters underground inspecting the No. 171 shaft of the mine in Wuming County, Nanning City, when two of them - Bi, the head of the mine, and He - passed out, an official surnamed Liao at Nanning's coal mine safety bureau said.

Pan rushed out of the mine to call for help but the two were dead by the time rescuers arrived.

Production in No. 171 shaft was supposed to have stopped two years ago when an exploitation license expired.

As no one was permitted to enter the disused shaft, the company may have been mining illegally, Liao said.

The Nanning City Government has ordered an investigation to determine the cause of the accident.