American climber Tyler Andrews set a new speed record using supplementary oxygen on Mount Everest on Thursday, his team told AFP, summiting the world's highest peak an hour quicker than anyone before.

Andrews, 36, a native of Concord, Massachusetts, climbed the 29,032-foot peak in just 9 hours and 55 minutes, shattering the record of 10 hours and 56 minutes held since 2003 by Nepali climber Lhakpa Gelu Sherpa.

The time requires formal verification by Nepal's mountain authorities.

Andrews summited Everest just before dawn on Thursday, according to posts on his Instagram, which included live GPS tracking of his route.

"He reached Everest's peak in just 9 hours 55 minutes," team leader Dawa Steven Sherpa of Asian Trekking told AFP.

The Asian Trekking team said that Andrews completed a solo climb, during which guides provided supplementary oxygen, food and water while tracking his ascent.

He had initially tried to break the 22 hours and 29 minutes speed record to climb Everest without supplementary oxygen earlier in May, but had to turn back.

"I've been training as an athlete all the way from high school cross country to running marathons to running in the mountains and, you know, Mount Everest is kind of the pinnacle of all of that," Andrews told CBS Boston last month while he was training in Wellesley, Massachusetts.

Andrews, who said he is a cancer survivor, is raising funds to support youth athletes who lack access to coaching and equipment in Ecuador and Nepal.

More than 950 climbers have reached the top of Everest this season, with the weather window rapidly coming to a close.

Five people have died this season -- two Indians and three Nepali climbers involved in Everest preparations.

That compares to the 18 people who died in 2023, the deadliest season on the mountain.

A U.S. and a Czech climber died on Mount Makalu earlier this month.

Nepali climber Kami Rita Sherpa, who scaled Everest for a record 32nd time earlier this month, returned to the capital Kathmandu on Friday, where he expressed concern about the experience of some climbers.

Pictures posted by climbers show a long line of people climbing up fixed ropes, queueing in the icy, low-oxygen high-altitude zones.

"It was very crowded this year compared to last year because there was more clients," Kami Rita Sherpa told reporters at Kathmandu airport after flying back from the mountain. "There is a need for authorities to control this number."