Rescuing 41 workers trapped in a highway tunnel in the Indian Himalayas for two weeks will take much longer than previously hoped as rescuers are switching to manual drilling following damage to machinery, officials said on Saturday.

The heavy drill brought in to break through nearly 60 metres of debris was damaged on Friday and was being pulled out entirely, government officials said, adding the last 10-15 metres would have to be broken with hand-held power tools.

The men, construction workers from some of India's poorest states, have been stuck in the 4.5-km tunnel being built in Uttarakhand state since it caved in early on November 12. Authorities have said they are safe, with access to light, oxygen, food, water and medicines.

A heavy drill machine, called an auger, which got damaged after hitting an obstacle on Friday, broke while being pulled out of the 47-metre pipe inserted to bring out the trapped workers.

Pushkar Singh Dhami, chief minister of Uttarakhand state said on Saturday the damaged drilling machine would be taken out by Sunday morning, allowing manual drilling to start.

Syed Ata Hasnain, a member of the National Disaster Management Authority which is overseeing rescue efforts, said the operation was becoming "more complex" and the process would become slower, compared to when the auger was used to drill.

"We have to strengthen our brothers stuck inside. We need to monitor their psychological state, because this operation can go on for a very long time," he said, without giving a timeline.

On Saturday morning the trapped workers, all migrants, were "very worried", said Sunita Hembrom, whose brother-in-law Birendra Kishku, 39, is in the tunnel.

"My brother in law told me that he has hasn't eaten any food since yesterday. We are very worried," she said.

Authorities have not said what caused the tunnel collapse, but the region is prone to landslides, earthquakes and floods. (Reuters)