Two missing climbers are believed to be dead after part of an icy ridge collapsed on Mount Everest during a lethal week on the world’s tallest peak.

British climber Daniel Paterson, 39, and his Nepali guide Pas Tenji Sherpa, 23, are still unaccounted for days after a cornice – a chunk of hardened snow overhanging the edge of a cliff — suddenly came down Tuesday, dragging climbers down the side of the crowded mountain, The BBC reported.

The pair were with a 15-person group that had reached the top of the world’s tallest peak at 29,032 feet.

Mount Everest adventure company 8K Expeditions, who organized the expedition, said they, “were caught in a sudden cornice fall, which impacted the group of climbers.”

Despite exhaustive search efforts, we regret to confirm that Daniel and Pastenji were unable to be recovered,” the company wrote in a memorial Instagram post Thursday.

The collapse happened around 4:40 a.m. on Tuesday near the Hillary Step as Paterson and Sherpa were making their descent. 

Videos posted on social media appears to show a line of hundreds of climbers stranded in the aftermath.

That area is considered part of Everest’s “death zone” over 26,000 feet, where oxygen levels and air pressure can be fatal over extended periods of time.

Sherpa, “a premier guide” at the company, had reached the peak of Everest twice, in addition to scaling K2, Ama Dablam and a number of other notable 6,000-meter (19,600-foot) peaks, 8K expeditions said.

Paterson, a CrossFit co-owner from Wakefield, had successfully summited Island Peak and Ama Dablam.

Paterson’s partner, Becks Woodhead, has raised more than $128,000 to launch a recovery mission for his body.

In a separate incident, 40-year-old Kenyan climber Joshua Cheruiyot Kirui, was found dead and his 44-year-old guide Nawang Sherpa remains missing after they vanished from the mountain on Wednesday.

Nepalese newspaper the Himalayan Times reported that Sherpa told base camp that Kirui had shown “abnormal behavior” and “refused to return and even consume bottled oxygen” before they disappeared. Officials lost contact with the team shortly thereafter.

Kirui’s close hiking friend, Kipkemoi Limo, told the BBC that he died in a fall. His body was found more than 60 feet below the mountain’s peak. 

“I have found myself shedding tears this morning after confirmation that my brother @cheruiyot_ak has rested on the mountain,” fellow climber James Muhia tweeted on Thursday. “It is a sad day. Our brother is now one with the mountain. It will be a difficult time. Go well my brother.”

Gabriel Tabara of Romania was also found dead inside his tent at Camp III on Tuesday, according to the Himalayan Times.

Two Mongolian climbers, Usukhjargal Tsedendamba and Prevsuren Lkhagvajav, also died in the death zone while descending the summit on May 13.

The increasing prevalence of deaths on Everest has been blamed on overcrowding and climate change.