A glacier in the Himalayas broke today and swept away a hydroelectric dam in northern India that is thought to have perished 150 people.

"The official number has not been confirmed" but between 100 and 150 people may have died, said Om Prakash, Chief of the Uttarakhand State Bureau where the ice break occurred.

One witness said he witnessed dust, rock and water merging like an avalanche crashing into the valley of the Dhauli Ganga River, about 500 kilometers north of New Delhi, India.

"It happened very quickly, with no time to warn people," said Sanjay Singh Rana, villager of Raini Chak Lata village in the upper Dhauli Ganga River.

Uttarakhand Ashok Kumar state police chief said more than 50 people working at a dam under the Rishiganga Hydropower Project may have died.

Indian Prime Minister Narendra Modi said he was monitoring the situation closely.

"India stands side by side with Uttarakhand and the whole country pray that everyone here will be at peace," he wrote on Twitter after speaking to Trivendra Singh Rawat, Premier of State.

The federal government announced that the Indian Air Force was ready to assist with rescue operations.

Neighboring Uttar Pradesh, India's most populous state, has placed riverside areas on high alert.

Videos posted online show water overflowing from a glacier sweeping everything in its path.

The Uttarakhand region in the Himalayas is a place prone to flash floods and landslides.