(AFP) - Rescuers in northern India battled for a second day Monday to save 40 workers trapped underground after the road tunnel they were building collapsed, bringing down tonnes of debris.

Teams using heavy excavators have been working nonstop since the collapse early Sunday morning to clear piles of concrete and earth, but with more debris falling as workers tried to clear a passage, a giant steel pipe was being prepared as an escape route.

"All the 40 workers trapped inside the tunnel are safe," Karamveer Singh Bhandari, a senior commander in the National Disaster Response Force, told AFP from the site in the Himalayan state of Uttarakhand, adding that water and food had been sent.

Oxygen was being pumped into the blocked portion of the tunnel, with food sent through a water pipe.

Rathodi said excavators had removed about 20 metres (65 feet) of heavy debris, but the men were 40 metres beyond that point.

"Due to excess debris in the tunnel, we are facing some difficulty in the rescue, but our team is leaving no stone unturned," Bhandari added.

Teams plan to use a heavy machine to drive a steel pipe with a width of 90 centimetres (nearly three feet), wide enough for the trapped men to squeeze through, the government's highway and infrastructure company said.

"Water, food, oxygen, electricity all are available with the work force trapped inside the tunnel... All the stranded workers are safe as communicated by them," the statement added.

Initial contact was made via a note on a scrap of paper, but later rescuers managed to connect using radio handsets.

"Some small food packets were sent in through a pipe which is also taking oxygen inside," rescue official Durgesh Rathodi told AFP from the site.

- 'Bring them out safely' -

Uttarakhand chief minister Pushkar Singh Dhami, who on Monday flew to the site of the accident, said on X, formerly Twitter, that the work to remove the tumbled concrete debris was "being made continuously to bring them out safely".

"Contact has been made with the workers trapped in the tunnel through a walkie-talkie," he said. "Efforts are being made to get them out safely soon."

One rescue worker, quoted by the Press Trust of India news agency, said the men were contacted shortly after midnight on Monday.

Disaster response official Devendra Patwal said that while the men were trapped, they had space in the tunnel area where they were.

"The good thing is that the labourers are not crammed in, and have a buffer of around 400 metres to walk and breathe," Patwal told the Indian Express newspaper.

The 4.5-kilometre (2.7-mile) tunnel is being constructed between Silkyara and Dandalgaon to connect two of the holiest Hindu shrines of Uttarkashi and Yamunotri.

Photographs released by the government rescue teams showed huge piles of rubble blocking the wide tunnel, with twisted metal bars on its broken roof poking down in front of the rubble.

The tunnel is part of Prime Minister Narendra Modi's road project aimed to improve connectivity for some of the most popular Hindu shrines in the country, as well as areas bordering China.

Accidents on large infrastructure construction sites are common in India.

In January, at least 200 people were killed in flash floods in ecologically fragile Uttarakhand in a disaster that experts partly blamed on excessive development.

© Agence France-Presse