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.

The emergency vehicles, seen shortly before dawn by AFP journalists at the site, were preparing to transport 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 rapped 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'-

Just before midnight, senior rescue team member Harpal Singh told reporters that engineers would enter the pipe to cut the rods, "following which we would use the (drilling) machine again".

Singh suggested a Thursday morning breakthrough was possible, although the government also warned that 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" as he arrived at the site on Wednesday evening.

"Work is being done at a fast pace," he said in a statement.

- 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 have 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 a Prime Minister Narendra Modi 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.

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