All 40 workers trapped in an under-construction tunnel on the Char Dham route are safe and being sent food and water, authorities assured Monday but said the rescue operation could take up to two more days.

A portion of the tunnel under construction between Silkyara and Dandalgaon on the Brahmakhal-Yamunotri national highway collapsed in the early hours of Sunday.

All workers trapped are safe and communicating, officials said on Monday as Chief Minister Pushkar Singh Dhami visited the site.

While oxygen started being supplied to the trapped labourers immediately after the launch of rescue operations on Sunday, they could only get drinking water and light food after contact was first established with them past midnight.

Secretary Disaster Management Ranjit Kumar Sinha who visited the tunnel said the trapped labourers could be rescued by Tuesday night or Wednesday.

The rescue strategy is now focused on stabilising loose muck by shotcreting (concrete spraying) and pushing in a large diametre steel pipe through the rubble to evacuate trapped workers.

Loose muck falling constantly from above clogs the excavated area, slackening the progress of rescuers. So it needs to be stabilised through shotcreting, an official engaged in the operations said.

"About 15-20 metres of rubble has been removed so far and the process is on. We plan to push in a steel pipe of 800 MM diametre by boring a hole into the heap of debris. We hope to rescue the trapped by Tuesday night or Wednesday," the secretary of disaster management told reporters in Silkyara.

The first communication with the labourers was established through wireless past midnight on Sunday, Circle officer Prashant Kumar said.

NHIDCL Director Anshu Manish Khalkho said the rescuers have contacted the labourers several times since through a pipe meant to supply food to them.

Rescuers who worked overnight trying to prepare an escape passage for the labourers have sent them dry fruits, among others food, he said.

"We are trying out all options to secure their early and safe evacuation. We have a plan A, plan B and plan C ready and are progressing accordingly," Khalkho said.

The collapsed area is spread over 30 metres and located 270 metres inside the tunnel from the Sikyara side, an official statement released from state capital Dehradun said.

The tunnel, supposed to be 4,531 metre-long when ready, is already built 2,340 metres from Silkyara side and 1,750 metres from Barkot side.

A technical committee headed by Uttarakhand Landslide Minimisation and Management Centre is looking into the circumstances that led to the partial collapse of the tunnel following a landslide, the release said.

According to a list of the trapped workers issued by the District Emergency Operation Centre, 15 are from Jharkhand, eight from Uttar Pradesh, five from Orissa, four from Bihar, three from West Bengal, two each from Uttarakhand and Assam, and one from Himachal Pradesh.

Dhami during his visit told reporters that all efforts were being made for the safe rescue of all those trapped in the debris.

"Safely rescuing the trapped workers is our priority. The rescue operation is being carried out expeditiously. I want to assure the families of the trapped labourers that they will be rescued soon," he said.

The chief minister said the Centre and his government were working together to rescue the trapped labourers.

Prime Minister Narendra Modi has taken a detailed update on the rescue operations and assured of all possible help, he added.

Rescue efforts led by personnel from multiple agencies, including the National Disaster Response Force, State Disaster Response Force, Indo-Tibetan Border Police, and the Border Roads Organisation, have been on since Sunday morning.

District Magistrate Abhishek Ruhela went inside the tunnel Monday morning to review the rescue op and discuss the strategy to save the labourers.

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