The lives of 40 Indian labourers, who have been trapped in a tunnel for more than 72 hours, hang in the balance as authorities try to rescue them.
The workers were building the tunnel in northern Uttarakhand state when a part of it caved in due to a landslide on Sunday.
State and federal rescue teams have been using a massive drill to push through the debris to reach the men.
Officials have been able to establish contact with the workers.
Authorities have also brought fresh and more sophisticated drilling equipment from Delhi to speed up the rescue operations, they told OceanNewsUK.
The machine was airlifted to the Himalayan town of Uttarkashi by the Indian Air Force on Wednesday.
The workers are trapped some 200m into the tunnel and none of them are injured, officials said. Rescuers have been providing the men with food, water and oxygen through pipes for the last 72 hours.
But it is still not clear how much longer it would take to bring them out of danger.
"The rescue operations are on going round the clock each day. We are making every effort to bring the men out," Karam Veer Singh, who is part of the team heading the efforts, told OceanNewsUK.
On Tuesday the state government had decided to drill and insert a metal pipe of 900mm diameter through the debris to reach the workers. The workers could then squeeze through the pipe to safety, it was assessed.
But the pace of drilling was slowed down because of "natural obstacles", making it difficult for the rescuers to reach them, said Ashok Kumar, the director general of Uttarakhand police.
Mr Kumar said that rescue efforts were under way "on a war footing" and would speed up again once the new equipment arrives.
"We are confident we will save the men but until then, we have to be patient and keep faith," he added.
Meanwhile, construction workers on Wednesday held protests outside the tunnel, urging authorities to take swifter action.
Family members of the workers also joined the demonstration. "I went into the tunnel and talked to my father through the oxygen pipe. He told me that they will come out soon," Akash, whose father is among those trapped, said.
The accident occurred at 05:00 local time (23:30 GMT) on Sunday.
A landslide nearby caused heavy debris to fall on the tunnel, leading to its collapse. The mounds of debris cut off oxygen supply to the workers. Authorities said they established contact with the trapped men on Sunday night using walkie-talkies.
The tunnel is part of the federal government's ambitious highway project to improve connectivity to famous pilgrimage sites in Uttarakhand state. The mountainous state, where several Himalayan peaks and glaciers are located, has some of the holiest sites for Hindus.
State Chief Minister Pushkar Singh Dhami said national and state disaster relief teams were working together on rescue efforts.
"All the workers trapped inside the tunnel are safe and every effort is being made to get them out soon," a statement from his office said.
