Six coal miners suffocated to death in a fire in northern Vietnam, dpa quoted authorities as saying Thursday. The fire started at 11: 30 pm Wednesday (1630 GMT) at a coal mine belonging to Dong Vung company in Uong Bi town, Quang Ninh province, the Vietnam National Coal Mineral Industries Group said. An initial investigation showed the fire was caused by a gas explosion, said Pham Hong Thanh, head of Dong Vong's coal mine office. One worker was injured and being treated in hospital. Smoke was still rising from the mouth of the tunnel early Thursday, according to local news outlet Thanh Nien.