Soldiers plan to use a so-called “rat-hole mining” technique, digging by hand to clear the rocks and rubble over the remaining nine metres (29 feet), with temperatures plummeting in the remote mountain location in the Himalayan state of Uttarakhand.

Last week, engineers working to drive a metal pipe horizontally through 57 metres (187 feet) of rock and concrete ran into metal girders and construction vehicles buried in the earth, snapping a giant earth-boring auger machine.

The workers were seen alive for the first time on Tuesday, peering into the lens of an endoscopic camera sent by rescuers down a thin pipe through which air, food, water and electricity are being delivered.

Though trapped, they have plenty of space in the tunnel, with the area inside 8.5 metres high and stretching about two kilometres in length.