Officials at the site of the partially collapsed under-construction tunnel in Uttarakhand on Tuesday began using steel pipes to rescue workers trapped inside, The Indian Express reported.

The tunnel, located on the Brahmakhal-Yamunotri national highway, collapsed in the early hours of Sunday, leaving 40 workers trapped. The tunnel is part of the Char Dham Road Project to build all-weather roads in Uttarakhand.

Authorities are attempting to rescue the workers by inserting large-diameter mild steel pipes through the rubble by using auger drilling machines. Auger drilling involves using a screw-shaped tool to make holes into the ground or other surfaces.

The National Disaster Response Force, State Disaster Response Force, the police and the fire brigade are conducting rescue operations.

Uttarkashi Circle Officer Prashant Kumar said on Monday that all the workers were safe and were being supplied with oxygen through a pipe. The authorities have also sent food and water to them, he added.

On Monday, rescue workers were able to cut through around 20 metres of debris out of a total of 55 metres to 60 metres. However, soil caved in the area again. This reduced the excavated portion to 14 metres, according to the Hindustan Times.

The Uttarakhand government has formed a six-member expert committee to investigate the causes of the accident, ANI reported.

The trapped workers hail from Bihar, Himachal Pradesh, Jharkhand, Odisha, Uttarakhand, Uttar Pradesh and West Bengal, officials said.

Jharkhand Chief Minister Hemant Soren said that his government will send a three-member team to assist the rescue operation.