A number of heavy machinery are seen parked at the entrance to the site of an under-construction road tunnel in Silkyara on Wednesday. AP

Indian rescuers have drilled three-quarters of the way through debris towards 41 workers trapped in a collapsed road tunnel for the past 11 days, officials said on Wednesday, raising hopes of a breakthrough with diggers in the final stretch.

Engineers are working to drive a steel pipe through at least 57 metres of the tonnes of earth, concrete and rubble that has divided the trapped men from freedom since a portion of the under-construction tunnel in the northern Himalayan state of Uttarakhand collapsed 11 days ago. Looking into the Silkyara tunnel entrance on Wednesday, a journalist could see sparks flying as workers welded metal tube sections together, with the site busy as excavators and heavy trucks brought in equipment.

Ambulances were on standby near the entrance, ready in the hope that the trapped men could soon be freed. Uttarakhand chief minister Pushkar Singh Dhami said the work was on a "war footing" as he arrived at the site on Wednesday evening.

"Work is being done at a fast pace," he said in a statement, saying engineers had drilled 45 metres through the 57 metres of debris, making a sudden rapid advance after days of painfully slow progress.

"If there is no blockage, we hope there could be happy news late tonight or tomorrow," Mahmood Ahmad, a road and highways ministry official involved in the operations, told reporters at the site. But a government statement also noted that "timelines provided are subject to change due to technical glitches, the challenging Himalayan terrain, and unforeseen emergencies."

Amid ongoing efforts to rescue 41 trapped workers from Uttarakhand's Silkyara tunnel, Prime Minister Narendra Modi on Wednesday once again spoke to Chief Minister Pushkar Singh Dhami over the phone and enquired about the ongoing operation to get them out safely.

Taking to X, Dhami said that he informed the Prime Minister about the positive progress made in the past 24 hours. "Prime Minister Narendra Modi ji spoke on the phone today and took information about the ongoing rescue operations to provide food, medicines and other essential items to the workers trapped in the tunnel under construction in Silkyara, Uttarkashi and to get them out safely," he posted.

"We are receiving continuous guidance from the Prime Minister to deal with this difficult situation, which provides new energy to all of us every day to take out the labor brothers quickly and safely with full strength," he added.

Rescue efforts have been slow, complicated by falling debris as well as repeated breakdowns of crucial heavy-drilling machines. The giant earth-boring machine last week ran into boulders, and drilling was put on hold for more than three days after a cracking sound in the roof. In case the route through the main tunnel entrance does not work, blasting and drilling have also begun from the far end of the unfinished tunnel, nearly half a kilometre long.

Preparations have also been made for a risky vertical shaft directly above. On the forested hill above, rescuers have cut an entirely new track to bring heavy equipment above the men, where a machine to dig an 89-metre vertical shaft is being installed — a complex dig above the men in an area that has already suffered a collapse.

The workers were seen alive for the first time on Tuesday, peering into the lens of an endoscopic camera sent by rescuers down a thin pipe through which air, food, water and electricity are being delivered. Though trapped, they have plenty of space, with the area inside 8.5 metres high and stretching about two kilometres in length.

Bhaskar Khulbe, a senior government official overseeing rescue efforts, said he had spoken to the trapped men on Wednesday morning. "All of them are in high spirits," he said.

The tunnel is part of Modi's infrastructure project aimed at cutting travel times between some of the most popular Hindu sites in the country, as well as improving access to strategic areas bordering rival China. But experts have warned about the impact of extensive construction in Uttarakhand, large parts of which are prone to landslides.

Agencies