LUCKNOW: Rescuers in north Indian mountains trying to reach 40 road workers trapped in a collapsed tunnel for more than three days will soon get help from a heavy drilling machine airlifted in to the site, officials said on Wednesday.

The workers are safe and rescuers have been able to communicate with them and send them food, water and oxygen through a pipe since the early Sunday collapse, but huge boulders have stymied efforts to dig an escape route for them.

A high-powered augur drilling machine has been airlifted from New Delhi, about 400 km to the south, in the hope of drilling through the debris trapping the men.

"The new machine has reached the nearest helipad. It is being assembled, and will be sent to the site soon,” said the head of police in India's northern state of Uttarakhand, Ashok Kumar.

The men were working on the Char Dham highway, one of the most ambitious projects of Prime Minister Narendra Modi's Hindu nationalist government, which aims to connect four Hindu pilgrimage sites in the mountains through 890 km (550 miles) of roads at a cost of $1.5 billion.

There were up to 60 men on the night shift in the 4.5-km (3-mile) tunnel, when the tunnel collapsed before dawn.

Men near the end of the tunnel managed to get out in time but the 40 trapped men were working deeper inside.

The ANI news agency showed footage on Wednesday of about a dozen angry workers outside the tunnel calling for their colleagues to be rescued quickly.

India's Himalayas are prone to landslides, earthquakes and floods. Geologists, residents and officials have blamed rapid construction for causing subsidence on slopes.

The road project has faced criticism from environmental experts and some work was halted after hundreds of houses were damaged by subsidence.

Work on the tunnel began in 2018 and was initially meant to be finished by July 2022. It had been due to be completed in May next year, the government said in a statement before the collapse.