The rescue operation to evacuate 41 trapped workers in a Uttarakhand tunnel for 15 days received another major blow as the giant drill working on their rescue collapsed. The Indian Army was called in to join the operation and was tasked with the manual drilling.

The blades of the auger machine got stuck in the debris as it was drilling through the rubble of the collapsed Silkyara tunnel.

The heavy drill brought in from America to break through nearly 60 meters of debris was damaged on Friday and is now being pulled out.

There are still the last 10-15 metres that need to be broken with hand-held power tools to evacuate the trapped workers.

Manual drilling would involve a worker entering the already bored stretch of the rescue passage, drilling for a brief period in the confined space, and then coming out to let someone else take over. Indian Army will helm the manual drilling.

A unit of Madras Sappers, an engineer group of the Corps of Engineers of the Indian Army, arrived at the site to assist in the rescue operations.

Trapped for over 360 hours, the 41 men may now have to wait for several more days, maybe weeks, before they are brought out safely.

Authorities have said they are safe, with access to light, oxygen, food, water and medicines.

The labourers have been trapped in a 400-metre buffer zone of the unfinished main tunnel since November 12 when a portion of the 4.5-km tunnel on the Brahmakhal-Yamunotri National Highway collapsed.

The tunnel - meant to join Silkyara and Dandalgaon in Uttarkashi - is a part of the Char Dham project.

The cause of the tunnel collapse has not been revealed by authorities.

Located in the Himalayas, the area is susceptible to landslides, earthquakes, and floods.