Forty-one workers remained trapped in a collapsed road tunnel in northern India for a seventh day as a new drilling machine arrived on site to replace the damaged one.

The nature of the exceptionally hard rock formation in the area coupled with the clearing of debris damaged the original machine and paused rescue efforts on Friday, according to officials. This added a new challenge to the long-drawn rescue efforts.

The number of trapped workers was also revised to 41 from 40, said Anshu Manish, a director at the National Highways and Infrastructure Development Corporation, one of the agencies overseeing the rescue.

He said the construction company building the tunnel, Navayuga Engineering Company, came to know about this discrepancy on Friday.

Authorities began drilling into the rubble and debris on Thursday and have so far covered a stretch of 24 metres, said Devendra Patwal, a disaster management official.

It may require up to 60 metres of drilling to enable the trapped workers’ escape, Mr Patwal told The Associated Press.

On Saturday, a team of experts held a meeting to also discuss other potential methods to rescue the trapped workers amid concerns that the drilling machine’s high-intensity vibrations could cause more debris to fall and hinder efforts.

Earlier, rescuers had hoped to complete the drilling by Friday night and create an escape tunnel of pipes welded together. But rescue efforts hit a snag after a loud cracking sound came from within the tunnel, startling those overseeing the operation, who paused the drilling after they found parts of the machine damaged, Tarun Kumar Baidya, director at NHIDCL, said from the site.

As the rescue operation stretched into its seventh day, families of those trapped were frustrated and angry. Relatives from various states have spent nights near the tunnel, seeking updates. The recent setback has only exacerbated their worries.

Krishna Patel, whose 20-year-old nephew is among the trapped, had hoped to see his relative on Friday.

“The administration keeps changing the timeline for when they may be rescued. It’s very frustrating,” he said.

Some of the workers felt fever and body aches Wednesday, but officials have said there has been no deterioration in their condition. Nuts, roasted chickpeas, popcorn and medicine were sent to them via a pipe every two hours.

Mr Patwal said two doctors at the site were in regular contact with the trapped workers to ensure their physical and mental wellbeing.

“We are trying our best to keep the spirit of the trapped labourers high because it is a trying time for all — the rescuers as well as the trapped people,” he said.

The construction workers have been trapped since Sunday when a landslide caused a portion of the 2.8-mile tunnel they were building to collapse about 200 metres from the entrance. The hilly area is prone to landslides and subsidence.

The site is in Uttarakhand, a mountainous state dotted with Hindu temples that attract many pilgrims and tourists. Highway and building construction has been constant to accommodate the influx.

The tunnel is part of the busy Chardham all-weather road, a flagship federal project connecting various Hindu pilgrimage sites.