More than a hundred rescuers in northern India struggled for a third day on Tuesday to save workers trapped underground after the road tunnel they were building collapsed.

Excavators have been removing debris since Sunday morning from the site in the Himalayan state of Uttarakhand to create an escape tunnel for the 40 workers, who are all alive.

"Our biggest breakthrough is that we have established contact and there is a supply of oxygen and food," Uttarkashi district's top civil servant Abhishek Ruhela told AFP on Tuesday.

"Whatever is necessary for their survival is being done."

Oxygen was being pumped into the tunnel and small food items such as dry fruit were being provided to the workers, he added.

The State Disaster Response Force (SDRF) said Tuesday rescuers had spoken to the trapped workers via radio.

Ranjit Kumar Sinha, a senior disaster management official, told reporters at the site he was hopeful workers could be freed by Wednesday, adding that there was enough oxygen where they were trapped "for about five to six days".

- 'Huge amount of debris' -

Construction worker Hemant Nayak told AFP that he had been in the tunnel early on Sunday when the roof caved in, but he had been on the right side of the collapse and escaped.

Small amounts of dirt had been falling into the tunnel, but "everyone took it lightly", he said.

"Then suddenly a huge amount of debris came and the tunnel was closed," he added.

Photos released by government rescue teams soon after the collapse showed huge piles of rubble blocking the wide tunnel, with twisted metal bars from its roof poking down in front of slabs of concrete.

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

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

The tunnel is part of Prime Minister Narendra Modi's road project aimed at improving travel conditions between some of the most popular Hindu shrines in the country as well as areas bordering China.

Accidents on large infrastructure projects 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.