One worker escaped with burns after the fire erupted yesterday night, and the bodies of six others who died of suffocation were pulled out today morning, said Duong Quang Lai, director of the Uong Bi Coal Co in Quang Ninh province.
Authorities today were still trying to put out the fire at the tunnel, which is between 30-105 metres deep, he said.
An investigation is underway.
The province is Vietnam's main coal-mining region. Dozens of workers have been killed in the past decade in mining accidents there.