GUIYANG, April 18 -- A roof collapse at a coal mine in southwest China's Guizhou Province in the early hours of Friday has killed seven miners and injured another.

The accident occurred around 12:45 a.m. when 13 miners were working underground at the Wantian Coal Mine in Liupanshui City, according to sources with the work safety authorities.

Six of them managed to escape. The injured miner is receiving treatment in hospital and his injury is not life-threatening.

An investigation into the cause of the accident is under way.

The Wantian Coal Mine is a privately owned colliery with an annual production capacity of 450,000 tonnes.