About 70-80 workers were 600-700m underground during a shift change at the small privately owned operation at the time of the explosion, with only two managing to escape.

Few survivors are expected as rescue efforts are hampered by at least five cave-ins caused by the blast.

The access tunnel, which is 2 kilometres long and up to 150m deep, collapsed in several areas.

Dow Jones Newswires reported that some 40 miners were still unaccounted for, while the explosion even destroyed the entry point of the tunnel.

A persistent build up of methane and carbon monoxide is also preventing rescue efforts, according to Associated Press.

The mine lacked gas detectors according to government officials.

The small thermal coal operation produces around 240,000 tonnes a year, while the coal company that owns the mine has not yet been named in the various reports.

Five miners reportedly died in a flood at the mine two years ago.