Rescuers attempted to excavate debris from a mountain tunnel in Uttarkashi on Monday, as part of efforts to save as many as 40 trapped construction workers. (Pushkar Singh Dhami/Twitter (X))

New Delhi (CNN) — A frantic effort is underway in northern India to rescue dozens of workers trapped after a mountain tunnel they were helping to construct collapsed on Sunday, leaving them confined behind a pile of rubble with little oxygen and water.

As many as 40 men were working in the tunnel, part of an ambitious Himalayan highway project in town of Uttarkashi, when part of the passageway leading to the entrance gave way, authorities said.

“We are in touch with the men inside. All of them are alright and we are communicating with them,” he said. “We are all working hard to get them all out,” Uttarkashi superintendent of police, Arpan Yaduvanshi, told CNN on Monday.

Rescuers have been supplying oxygen and water to the men through the debris, Yaduvanshi added.

Photos and video from the scene showed a large machine excavating debris from the dark tunnel as dozens of rescue officials gathered by the entrance. State and national disaster officials have come together to assist with the operation, alongside local police officials.

Uttarkashi Circle Officer Anuj Kumar said workers have removed about 20 meters (65 feet) of debris and have another 40 meters (130 feet) to go.

“It would take approximately another day or so to clear it up,” he said.

The tunnel is part of Indian prime minister Narendra Modi’s Char Dham Highway project, a multimillion-dollar infrastructure plan to improve connectivity in the state of Uttarakhand and better access to important pilgrimage locations.

Uttarakhand, a mountainous and picturesque state on India’s border with China, is often referred to as “Devbhumi” or “Land of the Gods” owing to its rich cultural heritage and the abundance of Hindu religious sites.

The Char Dham Highway project is expected to be nearly 1,000 kilometers (621 miles) long, improving access to the state from India’s capital New Delhi.

Sunday’s collapse isn’t the first construction disaster in recent months to make headlines in India, a country that has been rapidly transforming its infrastructure and spending billions to upgrade its transport network.

In August, more than a dozen workers were killed after a bridge under construction collapsed in the northeastern state of Mizoram.

In June, a four-lane concrete bridge that was being built across the River Ganges in the eastern state of Bihar collapsed for the second time in just over a year, raising questions about the quality of its construction.

Last October, a recently repaired suspension bridge gave way in the town of Morbi in Gujarat, killing 135 people.