A heavy-duty drilling machine flown in by the IAF from Delhi began boring through the rubble of a collapsed tunnel on the Char Dham route in Uttarakhand Thursday, in a fresh attempt to create an escape passage for 40 workers trapped inside for four days.

Workers outside the Silkyara tunnel performed a puja before the America-made auger machine began work.

Union Minister of State for Road Transport and Highways V K Singh had arrived at the site to take stock of the rescue operation when the drilling by the new machine began.

The Indian Air Force (IAF) had flown in the equipment in parts on their C-130 Hercules transport planes to an airstrip 30 kilometres away, after previous efforts to insert steel pipes into the rubble with the help of a smaller auger machine failed.

"I have been told that the new drilling machine has already penetrated 5-7 metres through the debris. We hope it would soon reach the trapped workers, drilling at the rate of 5-10 metres every hour," Chief Minister Pushkar Dhami told reporters in Dehradun.

Officials had earlier said that a 30-40 metre stretch of the under-construction had collapsed on Sunday. The collapsed section is 270 metres from the mouth of the tunnel from the Silkyara side. The workers are stranded on the other side of debris. They are safe, and being provided with oxygen, electricity, 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).

Sections of mild steel pipes of 800-mm and 900-mm diameter will be inserted -- one after the other -- into the drilled passage. Once this happens, the workers trapped inside can crawl out to safety.

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

The state government is providing all support to the technical experts supervising the rescue operations on the spot, Dhami said and added that they are in touch with international specialists.

He said Prime Minister Narendra Modi is constantly monitoring the situation.

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

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

The auger machine was flown in after the first drilling machine turned out to be too slow and technical issues developed, the officials said. Also, falling debris inside the tunnel damaged the first equipment and injured two rescue workers on Tuesday.

The 25-ton new auger machine has a capacity to drill 4-5 metres per hour, NHIDCL Director Anshu Manish Khalkho said earlier. After being brought to the site, the machine was installed through the night and made operational on Thursday. The portion of the tunnel, part of the ambitious Char Dham all-weather road project, collapsed due to a landslide on Sunday.

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