The shaft of the coal mine caved in some three miles (five kilometers) beneath the surface.

Experts differ on the cause of the collapse. Scientists had initially reported a mild earthquake in the region but have since suggested that the mine collapsed on its own, causing the seismic vibrations that were detected.

Mine owners contest this theory, saying that an earthquake caused the mine shaft to fail.

Early Friday a drill reached the cavity where the workers were believed to be trapped. Instruments lowered into the chamber detected sufficient levels of oxygen but detected no sound from the men.

''I wouldn't look at it as good or bad news," Bob Murray, chair of Murray Energy Corp.—the company that owns the mine—told the Associated Press.

"The work is not done.''

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