A coal mine gas leak left nine people dead in northwest China's Gansu Province Tuesday, local authorities said.

The accident happened at about 8:30 a.m. down the shaft of the Jinhe Coal Mining Company coal mine in Honggu District, Lanzhou City, the provincial capital, Wang Jianzhong, director of the Gansu Provincial Work Safety Administration, said.

Fifteen workers were in the shaft when the accident happened and six were evacuated safely, Li Guangjun, Party chief at Yaojie Coal and Electricity Group Co. Ltd. which owns Jinhe, said.

"After the emergency rescue operations, nine people trapped underground were confirmed dead," he said Tuesday afternoon.

He did not provide further details.

Local work safety authorities are investigating the cause of the accident.

State-owned Jinhe is a key coal producer with annual coal production capacity of 1.24 million tonnes.