Ambulances were on standby Thursday morning as Indian rescuers dug through the final metres of debris separating them from 41 workers trapped in a collapsed road tunnel for nearly two weeks.

Emergency vehicles and a field hospital stood ready, AFP journalists at the site said, preparing to receive the men who authorities hope will soon be freed from the tunnel in the Himalayan state of Uttarakhand.

Engineers have been digging for days to drive a steel pipe through some 57 metres (187 feet) of earth, concrete and rubble that has divided the trapped men from freedom since a portion of the under-construction tunnel caved in on November 12.

After days of painfully slow progress, engineers with a powerful drilling machine made a sudden rapid advance on Wednesday, before being slowed with just 12 metres (39 feet) to go after metal rods blocked the route.

- 'War footing'-

But after workers through the night crouched in the narrow area cut through the metal rods, the route was reopened for the earth-boring machine to drill the final section, Praveen Yadav, one of the rescue team told reporters on Thursday morning.

"We have cut and cleared the way," he said, adding the drill would restart to make the hoped for final push.

Rescuers are hoping for a breakthrough within hours, although the government has also repeatedly warned any timelines were "subject to change due to technical glitches, the challenging Himalayan terrain, and unforeseen emergencies".

Inside the Silkyara tunnel entrance, an AFP journalist said the site was a flurry of activity.

Worried relatives have gathered outside the site, where a Hindu shrine has been erected, with a priest holding prayers for the safe rescue of the trapped men.

"The day they will come out of the tunnel, it will be the biggest, happiest day for us," said Chanchal Singh Bisht, 35, whose 24-year-old cousin Pushkar Singh Ary is trapped inside.

Uttarakhand chief minister Pushkar Singh Dhami said the work was on a "war footing".

- Tough rescue -

Rescue efforts have been hampered by falling debris as well as repeated breakdowns of crucial heavy-drilling machines.

In case the route through the main tunnel entrance does not work, blasting and drilling were also begun from the far end of the unfinished tunnel, nearly half a kilometre (over a quarter of a mile) long.

Preparations have also been made for a risky vertical shaft directly above.

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.

The tunnel is part of Prime Minister Narendra 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.