Crews searching for any sign of six miners trapped for more than three weeks are “hoping a miracle could happen”, a US federal official told lawmakers.

Air quality tests in a section of a Mexican coal mine where as many as 26 miners could have been working have shown there is not enough oxygen to sustain life, it was announced early today.

Rescue workers chipped away at walls of debris separating them from 65 Mexican coal miners today, as family members desperate for word on their trapped relatives threatened to rush past soldiers guarding the pit.

A state commission is to examine mine safety and recommend changes to prevent accidents like the one that trapped nine men in a flooded coal mine for more than three days.