ZHENGZHOU - Four miners died, while nine others remain missing in a colliery gas outburst on Friday in central China's Henan Province, local authorities said.

The outburst happened at 10:37 a.m. in a 533-deep tunnel in Ruzhou City, where 250 miners were working underground, according to Li Yongsheng, assistant chief engineer of China Pingmei Shenma Group, shareholder of the coal mine.

Four miners were confirmed to have died as of 8:15 p.m., and rescuers are searching for the other nine, Li said.

The cause of the accident is under investigation.