Pakistani military helicopters continue to search for three missing climbers on the world’s second-highest mountain K2, as hope of their survival faded rapidly.

Muhammad Ali Sadpara, 45, of Pakistan, John Snorri, 47, of Iceland, and Juan Pablo Mohr, 33, of Chile, were last seen Friday about noon at what is considered the most difficult part of the climb: the Bottleneck, a steep and narrow gully just 300 metres shy of the 8611m high K2.

The spot is just above the ceiling of helicopters, which have been searching for three days.

Sadpara, one of Pakistan’s most celebrated climbers who had ascended eight of the world’s highest mountains, was accompanied by his 20-year-old son Sajid Sadpara, who was told by his father to climb down when his oxygen mask malfunctioned.

He told reporters on Sunday he waited overnight at a camp just below the Bottleneck, believing the three had reach the summit and would be coming down.

“I kept the light of my tent on at night thinking they would see it when they return,” he said.

It was the group’s second attempt at climbing K2 this winter, in a season that has already seen three other climbers die in the area.

Bulgarian Atanas Skatov’s body was picked up by a helicopter on February 5 and officials believe he fell while trying to climb K2.

Last month a team of 10 Nepali sherpas became the first people to reach the K2 summit in the winter.

The same day, Spaniard Sergio Mingote, 49, died after he fell down a crevasse attempting to make his way down to Base Camp.

Last month American Alex Goldfarb-Rumyantzev died trying to scale nearby Pastore Peak in preparation for attempting to reach the summit of Broad Peak.