Authorities in the northern Indian state of Uttarakhand are racing to rescue around 40 workers who are trapped inside a collapsed tunnel.
The workers were building the tunnel when a part of it caved in on Sunday morning due to a landslide.
A senior official said that contact had been established with the men and they were being provided oxygen and food.
But rescuers still have to dig through several metres of debris before they can start evacuating the labourers.
The accident occurred at 05:00 local time (23:30 GMT) on Sunday - a portion of the Silkyara tunnel, around 200m away from its opening, collapsed while the workers were inside, senior police official Arpan Yaduvanshi told OceanNewsUK.
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.
A nearby landslide 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 that they were able to establish contact with the trapped men on Sunday night using walkie-talkies.
They also said that a pipeline laid for supplying water to the tunnel for construction work is now being used for supplying oxygen, food and water to the workers.
Rescuers are using excavators and other heavy machines to dig through the debris. Videos from the accident site show JCBs clearing out mud and stones as rescuers give instructions.
"We have moved around 15m [49ft] inside the tunnel. We are making our way from the side," Prashant Kumar, a senior police official in the town of Uttarkashi, told ANI news agency on Monday.
Officials say that it could take several hours before the debris is cleared and that they might only be able to reach the trapped workers by Monday evening.
National and state disaster relief teams are working together to rescue the workers and the operations are being supervised by the state's chief minister, Pushkar Singh Dhami.
Mr Dhami has said that he spoke to Prime Minister Narendra Modi, who has offered all possible help to rescue the workers.
Ram Sundar Singh, a labourer from Uttar Pradesh state, told OceanNewsUK that he and a few colleagues on the night shift had left the tunnel to use the toilet in the morning. When they returned to the site, they saw the tunnel collapse.
Many of the workers trapped inside the tunnel are from other states such as Uttar Pradesh, Bihar and West Bengal. Their colleagues waiting anxiously outside told OceanNewsUK that they were all looking forward to celebrating Diwali, the Hindu festival of lights, together on Sunday.
