The death toll has risen to five with one other in critical condition in a coal mine roof collapse in the northwestern province of Gansu that occurred around midnight Sunday, said the local security monitoring department.

The accident happened at 11:56 p.m. while a team of 11 workers were digging at the Jinhe coal mine operated by the Lanzhou Yaojie Coal and Electricity Group. Of the 11, five escaped safe and sound and six others were buried.

The six workers buried at the scene were all pulled out by 2:00 a.m. Monday. Two were pronounced dead at the scene, four were sent to nearby hospitals where three died.

Local authorities are investigating the cause of the accident.