The bodies of eight people known to have died when they were engulfed in a wall of snow this week cannot be moved because of the storm that is continuing to pummel the Sierra Nevada range -- and the risk of yet more avalanches.

"Due to hazardous weather conditions, avalanche victims cannot be safely extracted off the mountain today," the Nevada County Sheriff's office said on Facebook.

"Recovery efforts are expected to carry into the weekend."

Six people survived Tuesday's tragedy, one of the deadliest avalanches in modern US history.

The group -- four guides and 11 paying clients -- was on their third day of a backcountry skiing trip on the 9,109-foot (2,776-meter) Castle Peak in the Lake Tahoe region of northern California, an area popular with mountain enthusiasts.

The six who survived -- five clients and a guide -- managed to call for help shortly after disaster struck, but white-out conditions and the risk of further snow slides meant rescue teams could not reach them for several hours.

Two had to be helped down, and were taken to hospital.

In the aftermath of the accident, questions have been asked about why skiers were out on the mountain in such difficult conditions, with several feet of snow falling and experts warning of the risk of avalanches.

Expedition organizers Blackbird Mountain Guides on Wednesday said all staff in the group were professionally trained, and urged people to avoid speculating about the circumstances.

"This was an enormous tragedy, and the saddest event our team has ever experienced. In addition to mourning the loss of six clients, we also mourn the loss of three highly experienced members of our guide team," company founder Zeb Blais said.

"Guides in the field are in communication with senior guides at our base, to discuss conditions and routing based upon conditions.

"There is still a lot that we're learning about what happened. It's too soon to draw conclusions, but investigations are underway."