A heavy-duty drilling machine bored through 12 metres of rubble of the collapsed tunnel on the Char Dham route in Uttarakhand on Thursday, raising hopes for the rescue of 40 workers trapped inside for over four days.

Officials said in the evening that a six-metre section of a steel pipe had been inserted into the bored passage. Another section was being welded into it.

The plan is to insert 800 mm- and 900 mm diameter pipes – one after the other -- with the help of the giant drill till an escape passage is created for the workers stranded beyond the collapsed portion of the under-construction tunnel.

After a smaller drilling machine failed to do the job, IAF’s C-130 Hercules planes brought the US-made auger machine, in parts, from Delhi to an airport 30 kilometres away on Wednesday. The 25-tonne piece of equipment was installed overnight.

Before making this fresh rescue attempt, a ‘puja’ was held outside the Silkyara tunnel on Thursday.

Union Minister of State for Road Transport and Highways V K Singh, who visited the rescue site, set “two of three days” as the “outer limit” for the new machine to get the job done.

But Uttarakhand Chief Minister Pushkar Singh Dhami, who said Thursday that all tunnel projects in the state will now be reviewed, appeared more optimistic.

"I have been told that the new drilling machine has already penetrated five to seven metres through the debris,” Dhami told reporters earlier in the day in Dehradun. “We hope it would soon reach the trapped workers, drilling at the rate of five to 10 metres every hour." At first, when the 30-40 metre portion of the tunnel collapsed on Sunday morning, rescue workers had tried excavating the rubble using an earth moving machine.

The stretch with the debris begins 270 metres from the mouth of the tunnel at its Silkyara side.

The trapped workers are safe, and being supplied with oxygen, medicines, food items and water through pipes, Navayuga Engineering Company's spokesperson G L Nath said. The company is building the tunnel on behalf of the National Highways and Infrastructure Development Corporation Limited (NHIDCL).

Union minister Singh talked to the trapped workers. “The people’s morale is high,” he told reporters later, adding that they knew that the government is putting in all efforts to get them out.

He said experts in the country and abroad have been consulted on the rescue operation.

The minister said the site where the tunnel is being constructed has been stable for the past four and a half years.

In Dehradun, the chief minister Dhami said Prime Minister Narendra Modi is constantly monitoring the situation.

The Uttarakhand government has decided to review all under-construction tunnels in the state, he said.

"We need such tunnels and many of them are being built in the state. We will review wherever they are being constructed," he added.

A six-bed makeshift health facility has been set up and 10 ambulances with doctors also stationed outside the tunnel to provide immediate medical care to the trapped workers on their evacuation, officials said.

Doctors have advised that the workers would need both physical and mental rehabilitation upon being rescued.

The victims might experience panic attacks because of being trapped in closed spaces for long, said Dr Ajay Agarwal, director, Internal Medicine AT Fortis Hospital in Noida.

"Further, the ambient conditions such as oxygen and carbon dioxide levels too could impact their physical health and prolonged exposure to cold underground temperatures could possibly cause hypothermia and make them fall unconscious," Agarwal told PTI.

The new auger machine was flown in after the first drilling machine turned out to be too slow and technical issues developed, officials said.

Also, falling debris inside the tunnel damaged the first machine and injured two rescue workers on Tuesday.

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