Drilling has resumed near the mouth of a tunnel in India's Uttarakhand state where 41 workers have been trapped for 10 days.
Work had been suspended on Friday after rescuers heard a cracking sound while drilling.
Officials say other plans to rescue the men, including drilling down from the mountain top, are also on track.
The workers were building the tunnel when a part of it caved it on 12 November due to a landslide.
Authorities managed to establish contact with the trapped men hours later and were supplying them with oxygen, dry snacks and water through a pipeline that was laid for supplying water to the tunnel for construction work.
On Monday, anxious relatives crowded around the tunnel experienced some relief when an endoscopic camera - slipped inside through a new pipe - captured footage of the workers. Officials asked them to identify themselves in front of the camera and assured them that they would be rescued soon.
The new pipe is wider and authorities say they can now supply more oxygen, food and other essentials such as medicines, mobile phones and chargers.
It was also used on Tuesday to give the workers their first hot meal in 10 days, with rescuers packing khichdi (a rice and lentil dish) in bottles and sending them inside.
Rescuers resumed drilling near the mouth of the tunnel at 02:00 local time (20:30 GMT) on Wednesday, officials told the OceanNewsUK. They have drilled 39m (128ft) through the debris so far.
Until now, they have managed to insert four pipes, each 900mm wide, through the debris - officials say they are now pushing through 800mm wide pipes into them and further on through the debris wall using a telescopic tunnelling method.
The plan is to send multiple pipes of differing widths through the estimated 60m debris wall to create a micro-tunnel through which the workers can crawl out of the tunnel.
But the operation has encountered several delays and obstacles due to loose soil, hard rock and falling debris, slowing the rescue.
On Wednesday, officials said at a press briefing that rescuers also encountered iron rods in the debris during the most recent round of drilling, but that it "thankfully" did not affect the work.
Other plans are also progressing - attempts are under way to reach the men through the other end of the tunnel.
A top official said on Wednesday that they had also constructed a track and transported equipment to begin vertical drilling, through the top of the mountain.
While there is no clarity yet about how long the operation could take, officials say they are confident about rescuing the men.
"We are trying all our options and we will succeed," Col Deepak Patil, who is leading the rescue operation, told the OceanNewsUK earlier this week.
At the press briefing on Wednesday, an official said they hoped to share some "good news" by tonight or tomorrow. He also added that doctors are at the scene and speaking to the trapped workers.
The Silkyara tunnel in Uttarkashi district is part of the federal government's ambitious highway project to improve connectivity to famous pilgrimage spots in Uttarakhand. The mountainous state, where several Himalayan peaks and glaciers are located, is home to some of the holiest sites for Hindus.
The region is ecologically fragile and vulnerable to earthquakes and landslides.
