Working round-the-clock with a powerful machine, rescue workers have drilled through up to 24 metres of rubble in the Silkyara tunnel till Friday afternoon, inching closer to the 40 labourers trapped inside for five days.

In its latest update on the rescue operation, the National Highways & Infrastructure Development Corporation Limited (NHIDCL) said the fifth pipe -- being used to prepare an escape passage for the trapped workers -- is being positioned.

The rescue workers have to drill up to 60 metres to insert 800- and 900- millimetre diameter pipes -- one after the other -- with the help of a giant drill till an escape passage can be created for the labourers stuck behind the collapsed portion of the under-construction tunnel, NHIDCL Director Anshu Manish Khalkho said.

Asked why the machine was not able to achieve the expected drilling speed of four to five metres per hour, he said aligning the pipes on the machine and welding those properly before pushing those through takes time.

Khalkho also claimed that the drilling machine being diesel operated is behind the the slow progress.

"It is a diesel-operated machine working in an enclosed space. So ventilation at certain time intervals with compressors is also needed. The vibration created by these processes may disturb the equilibrium," he said.

"We are working with a strategy but it has to be reinforced to ensure nothing goes wrong midway through," he said.

The machine has been working satisfactorily and the speed will go up as more progress is made through the rubble and the rescue workers get accustomed to the method, Khalkho added.

Another 'auger machine' is being airlifted from Indore as a back-up so that the rescue operation continues uninterrupted, he said.

Meanwhile, people whose relatives are among the 40 trapped workers are being allowed to speak to them through a pipe inside the tunnel.

Two people from Uttar Pradesh were allowed to speak to their kin, who are among the trapped workers.

"My nephew is among those trapped. I spoke to him. He said that he was fine," Shatrughan Lal said.

A man from Lahimpur Kheri in Uttar Pradesh, whose son Manjit is among those trapped, said he was happy to hear his voice.

"He asked me not to be tensed as he was doing well. The authorities have asked us to wait patiently. All I wish is that he comes out safely," he said.

Navayuga Engineering Company Ltd PRO GL Nath told PTI, "The trapped workers have been provided food. They are fine. The auger machine is also working well. We pray to god that they are evacuated as soon as possible." When asked about the progress of the work, he said the fifth pipe is being pushed in.

Each of the 900-millimetre diameter pipes being used to prepare an escape passage for the trapped workers is six metres in length.

An American auger drilling machine was flown in from Delhi on Wednesday to speed up rescue efforts as the earlier one deployed for the purpose had a capacity to penetrate only up to 45 metres of rubble, Adesh Jain, an expert overseeing the operation from the spot, said.

It had to be replaced by a heavier and more efficient drilling machine as the debris had spread over an area of about 70 metres due to rubble constantly falling from above, Jain said.

Consultations are also being held with international experts who have experience of being involved in similar rescue operations.

The round-the-clock rescue work is being helmed by 165 personnel from multiple agencies, including the National Disaster Response Force, State Disaster Response Force, Border Roads Organisation and the Indo-Tibetan Border Police, the State Emergency Operation Centre said.

The labourers have been trapped since Sunday morning when a part of the tunnel collapsed following a landslide.

The stretch where debris is accumulated begins 270 metres from the mouth of the tunnel on the Silkyara side.

Uttarkashi District Magistrate Abhishek Ruhela said the trapped workers are safe and being supplied with oxygen, medicines, and food and water through air compressed pipes.

Constant communication is being maintained with them to keep up their morale, he said.

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