New Delhi: A part of the Nanda Devi glacier broke off at Joshimath in Uttarakhand's Chamoli district on Sunday, leading to a massive flood in the Dhauli Ganga river and causing large-scale devastation in the upper reaches of the ecologically fragile Himalayas.

Over 150 labourers working at a power project in Tapovan-Reni are feared dead, an Indo Tibetan Border Police spokesperson said while quoting the project-in charge. Three bodies were recovered.

However later, SS Deswal, DG, ITBP informed, "It is suspected that around 100 workers were at the site. Of which, 9-10 dead bodies have been recovered from the river."

"There was an under constructed tunnel near Tapovan dam in Uttarakhand where around 20 workers are stranded." he added.

The power project was swept away completely, added state Director General of Police Ashok Kumar while describing the situation as under control.

The Army has been pressed into service to carry out rescue operations in flood-affected areas. The government has asked the Army to help district administration and disaster teams of the central and state government in their rescue operations. Further, Indian Air Force assets, both fixed wing as well as rotary, are on standby to provide all possible assistance to the affected persons.

Troops have been moved towards the flood-affected areas in Dhauliganga, where the massive flood occurred after the glacier broke.

The Army aviation wing has also been pressed into service to carry out an aerial survey and evacuate trapped people. "One advance light helicopter and two Cheetah helicopters are evacuating persons in the area," an Army official said.

Four columns of around 400 personnel of the Army have been moved to flood-affected areas, the official added.

"Indian Air Force C-130 and AN-32 aircraft are being used to airlift National Disaster Response Force (NDRF) personnel," said a senior IAF official.

Homes along the way were also swept away as the waters rushed down the mountainsides in a raging torrent. There were fears of damage in human settlements downstream, including in heavily populated areas. Many villages were evacuated and people taken to safer areas.

Connectivity with some border posts was "totally restricted" due to a bridge collapsing near Reni village, an ITBP spokesperson said.

Several districts, including Pauri, Tehri, Rudraprayag, Haridwar and Dehradun, that were likely to be affected were put on high alert and forces of the ITBP and the National Disaster Response Force (NDRF) rushed in to help with the rescue and relief effort.

I am constantly monitoring the unfortunate situation in Uttarakhand. India stands with Uttarakhand, prays for everyone's safety, Prime Minister Narendra Modi said.

News that the 150 labourers at the project on Rishi Ganga were affected had come in the early in the day.

Representatives of the power project have told me that they are not being able to contact around 150 of their workmen at the project site," said State Disaster Response Force DIG Ridhim Aggarwal. The waters in the Dhauli Ganga, a tributary of the Ganga, was flowing two to three metres above normal,the official added.

Union Home Minister Amit Shah spoke to Uttarakhand Chief Minister Trivendra Singh Rawat and assured him of all possible support to deal with the situation arising from the glacier burst and the resulting floods.

In a series of tweets in Hindi, Shah also said teams of the NDRF were deployed for rescue and relief operations of the affected people while additional troops of the force were being airlifted from Delhi.

"I have spoken to Chief Minister @tsrawatbjp ji, DG ITBP and DG NDRF regarding the natural disaster in Uttarakhand. All the concerned officers are working on a war footing to secure the people. NDRF teams have left for rescue operations. Every possible help will be provided to 'Devbhoomi'," he said.

Shah said the central government is constantly monitoring the situation in Uttarakhand.

"Some more teams of NDRF are being airlifted from Delhi and sent to Uttarakhand. We are constantly monitoring the situation there," he said.

A home ministry spokesperson said four NDRF teams (about 200 personnel) were airlifted to Dehradun and would head to Joshimath.

The chief minister also appealed to people to not spread rumours through old flood videos.

He said the water level in the Alaknanda, another tributary of the Ganga, is one metre above normal but the flow was reducing gradually.

He said all districts concerned have been alerted and people have been asked not to go near the Ganga.