India's military brought in specialised equipment on Sunday as efforts to free 41 trapped workers entered a third week, with digging ongoing in three directions after repeated setbacks to the operation.

The Indian air force said on Sunday that they were "responding with alacrity," as they flew in their third load to a rescue operation since the partial collapse of the under-construction Silkyara road tunnel on November 12 in the Himalayan state of Uttarakhand.

Rescue officials said they called for a superheated plasma cutter to be brought to the remote mountain location, after engineers driving a metal pipe horizontally through 57 metres of rock and concrete ran into metal girders and construction vehicles buried in the earth.

A giant earth-boring machine snapped just nine metres from breaking through.

The plasma cutting will be used to remove the broken giant earth-boring drill and metal blocking the horizontal route, before digging will continue by hand.

Thick metal girders in the rubble are blocking the route, and using conventional oxyacetylene cutters to clear them is tricky from inside the confined pipe, only wide enough for a man to crawl through.

The air force said the "critical" kit came from the country's Defence Research and Development Organisation, the government's defence technology research arm, without giving further details.

Uttarakhand chief minister Pushkar Singh Dhami said on Saturday that vertical drilling had begun to dig 89 metres downwards, a risky route above the men in an area that has already suffered a collapse.

Work has also begun from the far side of the road tunnel, a much longer third route estimated to be around 480 metres.

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.

Dhami said the men are in "good spirits", with a basic telephone exchange set up so that families of the trapped men – many of whom are migrant workers from poor families from far across India – could call in to speak to them.

Efforts have been painfully slow, complicated by falling debris and repeated breakdowns of drilling machines.

Hopes that the team was on the verge of a breakthrough on Wednesday were dashed, with a government statement warning of the "challenging Himalayan terrain."

Indrajeet Kumar told the Times of India he "feels like crying" when he speaks to his brother Vishwajeet, who is among the trapped workers, who questioned why they were still stuck after reports that they "would be out soon."

Syed Ata Hasnain, a senior rescue official and retired general, called on Saturday for "patience."

"A very difficult operation is going on," he told reporters.

"When you do something with mountains, you cannot predict anything," he added. "This situation is exactly like war." (AFP)