Three renowned mountain climbers are feared to have died after an avalanche in the Canadian Rocky Mountains.
American Jess Roskelley and Austrians David Lama and Hansjorg Auer were attempting to scale a challenging route up the east face of Howse Peak in Alberta's Banff National Park, Canadian officials said.
The group was last heard from on Tuesday morning, when Mr Roskelley spoke to his father, John Roskelley, himself a world-renowned climber.
Search efforts began on Wednesday when the climbers failed to check in as planned, and Parks Canada said a helicopter crew saw evidence of several large-scale avalanches which had engulfed climbing equipment.
Stephen Holeczi, Parks Canada’s visitor safety specialist, said there was “strong evidence” all three climbers had been killed, without going into further detail.
Mr Holeczi said the avalanche that hit the group rated three on a five-point scale, roughly strong enough to destroy a small building, or uproot several trees.
John Roskelley said the group had been attempting a route that was first conquered only in 2000.
“It's just one of those routes where you have to have the right conditions or it turns into a nightmare. This is one of those trips where it turned into a nightmare,” he told Washington newspaper The Spokane-Review.
The elder Mr Roskelley said he had climbed the 10,810-foot Howse Peak himself in the past and would travel to Canada in an attempt to help with the recovery effort.
The area where the climbers were presumed to have got into trouble was “above a basin”, he said. “There must have been a lot of snow that came down and got them off the face.
“When you're climbing mountains, danger is not too far away...It's terrible for my wife and I,” he said. “But it's even worse for his wife."
The younger Mr Roskelley, 36, was most famous for having climbed Mount Everest in 2003 at the age of 20, then becoming the youngest American to have scaled the world’s highest peak. His father John joined him on that climb.
Mr Lama, 28, was the subject of a documentary film in 2014 about his attempt to free-climb the Compressor Route on the Cerro Torre mountain in Patagonia, something never achieved before.
His father was a mountain guide from Nepal, and he won numerous climbing competitions as a teenager.
Mr Auer, 35, grew up near the Dolomites in Austria and was best known for completing the first ascent of the south face on Nilgiri South in Nepal.
The North Face, which sponsored the trio, said in a statement that the group were “missing, and local search and rescue has assumed the worst”.
“We are doing everything we can to support their families, friends and community during this difficult time,” the firm said.