An avalanche in Alaska backcountry swept up and buried three skiers under a blanket of snow that could be as deep as a 10-storey building, Alaska State Troopers said Wednesday.

While troopers have not been able to assess the site yet, "based on the information provided by the operator, unfortunately, we do not believe that any of the three missing persons survived the avalanche," Austin McDaniel, a spokesperson for the Alaska State Troopers, said in a text to The Associated Press.

If the deaths are confirmed, it would be the deadliest U.S. avalanche since three climbers were killed in a slide in Washington's Cascade Mountains two years ago.

The slide happened late Tuesday afternoon near the skiing community of Girdwood, located about 64 kilometres south of Anchorage, said McDaniel.

Guides from the heli-skiing company attempted to locate the skiers. Using avalanche beacons, the guides identified a probable area where the skiers were buried, at a depth of 12 to 30 metres, McDaniel said in a later email.

"The guides were unable to recover the three skiers due to the depth. Due to considerable avalanche risk in this area and limited daylight, no further recovery operations were conducted on March 4," he said. "If weather and conditions allow for it, Troopers plan to assess avalanche conditions from the air and determine recovery options with individuals that have experience making avalanche recoveries."

The avalanche site is about 13 kilometres northeast of the airport in Girdwood.

Girdwood is the skiing capital of Alaska, and home to the Alyeska Resort, at the base of Mount Alyeska, where people downhill ski or snowboard amid stunning views of Turnagain Arm. At the top of the mountain is the Seven Glaciers Restaurant, named for its view.

Heli-skiing is using a helicopter to reach the top of a mountain in remote backcountry areas where there are no ski lifts, and a person either skis or snowboards down the mountain.

Each winter, 25 to 30 people die in avalanches in the U.S., according to the National Avalanche Center.

Fifteen people have been killed across the U.S. by avalanches so far this winter. Among them were 10 backcountry skiers or snowboarders, four people on snow machines and a ski patroller, according to the Colorado Avalanche Information Center.

Colorado experiences the most avalanche deaths, with 325 people killed since 1950. Alaska ranks second, with 172 deaths in that time period, according to the centre.

In 2021, Czech billionaire Petr Kellner and four others died in a helicopter crash during a heliskiing tour near Knik Glacier, in the Chugach Mountains just north of Anchorage. A year later, a heli-ski guide scouting an area for clients died when an avalanche carried his body nearly 1500 feet (457 meters) down a mountain, Alaska State Troopers said at the time.