SILKYARA, India: Indian rescuers began drilling vertically on Sunday from the top of a mountain under which 41 workers became trapped two weeks ago while working on a highway tunnel in the Himalayas, government officials said.

The men, construction workers from some of India's poorest states, have been stuck in the 4.5-km (3-mile) tunnel being built in Uttarakhand state since it caved in early on Nov. 12. Authorities have said they are safe, with access to light, oxygen, food, water and medicines.

But rescuing them will take much longer than previously hoped as rescuers have switched to manual drilling following damage to the drilling machine, officials said on Saturday.

Rescuers had hoped to finish the drilling late on Thursday but had to suspend operation after the platform on which the machine was placed was damaged.

Work resumed on Friday evening only to be suspended soon afterwards as the machine ran into a new obstacle, officials said, without elaborating.

Vertical drilling started on Sunday and it will take about 100 hours, the officials said.

Initially, the rescue plan involved pushing a pipe wide enough to pull the trapped men out on wheeled stretchers.

The men have been getting cooked food via a lifeline pipe that was pushed through to ensure steady supplies of essential goods.

More than a dozen doctors, including psychiatrists, are at the site, talking to the men and monitoring their health. The fact that the tunnel is closed by the debris is keeping the men warm.

They have been told to do light yoga exercises, walk around in the two km of tunnel space they have been confined to, and keep talking to each other.

Deepak Patil, one of the officers in charge of the rescue mission, told Reuters authorities had sent in two mobile phones and memory cards with Hindi films and electronic games.

Priyanka Chaturvedi, a spokeswoman for one of India's opposition parties, on Sunday asked for an investigation into the accident and asked the government to ensure the safety of the men.

A member of a panel of experts investigating the disaster said on Friday the tunnel does not have an emergency exit and was built through a geological fault.