Indian officials have said the chances of finding eight missing climbers – including four Britons – alive in the Himalayas are “bleak”.
The group was attempting to reach the summit of India’s second-highest peak Nanda Devi in Uttarakhand.
The missing Britons have been named locally as group leader Martin Moran, John McLaren, Rupert Whewell and Richard Payne.
US nationals Anthony Sudekum and Ronald Beimel, Australian Ruth McCance, and Indian guide Chetan Pandey are also missing.
Two Indian air force helicopters and a rescue team have been searching the region for the group for two days now after the climbers failed to return to their base camp.
Other climbers in the group who had turned back earlier from the trek alerted the authorities on Friday night.
“The first aerial recce has concluded,” said Vijay Kumar Jogdanda, a civil administrator in Pithoragarh district in northern India’s Uttarakhand state.
“There were only tents spotted, but no human presence. The second helicopter has left for the recce.
“Chances of survival are bleak,” he added, and confirmed there had been an avalanche in the area which the climbers may have been caught up in.
The University of York confirmed that one of its lecturers – Dr Richard Payne – travelled to the Himalayas.
“We remain extremely concerned for his safety and our thoughts are with his family, friends and colleagues at this difficult time,” the university said in a statement.
Nigel Vardy, a mountaineer who has known Mr Moran for 20 years, said his friend is a “top of the range” climber who “knows the mountains, he knows the area, he knows what he is doing”.
But avalanches can catch even the most experienced climbers unaware, he told Sky News.
“Avalanche debris is incredibly heavy. It sets like concrete. You really don’t just walk out of this stuff,” he said.
Mr Moran’s family have released a statement saying they are “deeply saddened” by the unfolding incident.
They added: “As a family, we share the same emotions that all next of kin are experiencing in not knowing the whereabouts or well-being of those closest to us.”
The climbers, who began their ascent of Nanda Devi on 13 May, went missing on the Indian side of the Himalayas near the end of a climbing season during which there have been several fatalities.
At least nine people have died on the Nepalese side of Mount Everest this year, making it the deadliest climbing season on the peak since 2015.
A Foreign Office spokesperson said: “We are in contact with the Indian authorities following reports that a number of British nationals are missing in the Indian Himalayas.
“We will do all we can to assist any British people who need our help.”
Moran Mountain, which ran the expedition, said in a Facebook post on Sunday that it was working with authorities and the British Association of Mountain Guides to gather information about the expedition’s fate.
The statement from Mr Moran’s family added that it was “not entirely clear” what had happened to group, but that they had heard of another British mountain climber in the area who had initially gone to search for the group when they hadn’t returned to base camp.
“There was clear evidence that a sizeable avalanche had occurred on the mountain and it seemed to be on or very near the route that would be taken by the climbing group,” the statement said.
“The mountain guide gave instructions to base camp to alert rescue authorities. The alarm was raised early on Friday morning.”
In response to the coordinated search and rescue effort, the Moran family said they were “grateful”, but that they were hoping to widen the search area in order to find firm evidence “to ascertain the well-being or otherwise of all those in the climbing group”.