Hours after the late-morning calamity, as darkness fell and a nearby highway was closed due to zero visibility in the midst of a winter storm, a spokesperson for the Nevada County Sheriff’s Office, Captain Russell Greene, said rescue teams had yet to reach the avalanche site.

“It’s going to be a slow, tedious process because they also have to be very careful accessing the area because the avalanche danger is still very high,” Greene said in an interview with Sacramento-based television station KCRA-TV.

The avalanche swept the Castle Peak area of Truckee, California, about 10 miles north of Lake Tahoe, at about 11:30am Pacific time, engulfing a group of 16 skiers, according to a Facebook statement posted by the Nevada County Sheriff’s Office.

The group consisted of four ski guides and 12 clients.

At least six survived and remained at the avalanche site awaiting rescue, while the others were unaccounted for, the statement said.

‘High avalanche danger’

If all 10 of the missing skiers should perish, the incident would rank among the deadliest single avalanches on record in the United States.

The Colorado Avalanche Information Centre has tallied six US avalanche fatalities so far this season.

Avalanches have claimed an average of 27 lives each winter in the United States over the past decade, the centre reported.

A winter storm warning was in effect for much of northern California on Tuesday, with heavy snow forecast in the upper elevations of the Sierra Nevada.

The Sierra Avalanche Centre had posted an alert before dawn on Tuesday, warning of a “high avalanche danger” in the ski region, the sheriff’s statement said.

“I don’t think it was a wise choice,” Greene said of the decision of a ski tour company to take paying customers out into the backcountry under such conditions, adding, “but we don’t know all the details yet.”

He declined to name the company involved.

California Governor Gavin Newsom was briefed on the avalanche, and state authorities were “coordinating an all-hands search-and-rescue effort” in conjunction with local emergency teams, his office said in a posting on X.