A group of skiers on the final stretch of a three‑day backcountry trip near Lake Tahoe was returning to the trailhead Tuesday morning when a wave of ice, rocks and debris came crashing down on them.

In the avalanche’s wake, survivors were left scrambling to try and find the rest of their group — and to improvise shelter as they awaited rescue.

The disaster at Castle Peak set off a dangerous, hours-long rescue effort that was hampered by extreme weather conditions that were hammering the skiers: Heavy snow and strong winds from the winter storm roaring through the rugged Sierra Nevada mountains in northern California.

Emergency crews received reports of the avalanche around 11:30 a.m. and “highly skilled rescue ski teams” immediately began racing to the scene — 46 emergency first-responders in all, the sheriff said.

Eleven hours later, six survivors had been rescued with “various injuries,” the sheriff’s office said, noting two had to be transported to the hospital for treatment. Nine are still missing.

“The search is ongoing, pending weather conditions,” the Nevada County Sheriff’s Office said late Tuesday.

A race to reach the survivors

Snow falls on Tuesday in Truckee, California. Crews were looking for multiple backcountry skiers feared missing after a reported avalanche.

Snow falls on Tuesday in Truckee, California. Crews were looking for multiple backcountry skiers feared missing after a reported avalanche.
Brooke Hess-Homeier/AP

The area was under the second highest level, a 4 of 5, of avalanche threat Tuesday, which continued into the early hours of Wednesday.

Blackbird Mountain Guides, the company leading the trip, said the group included 12 clients and four guides who had been staying at the Frog Lake huts since Sunday.

The sheriff’s office said a total of 15 people were on the trip, revising the number down. CNN has reached out to Blackbird Mountain guides for clarification.

“The leadership team at Blackbird Mountain Guides is working in full coordination with the Nevada County Sheriff’s Office and Nevada County Search and Rescue to support the ongoing rescue operation,” the company said in a statement. “Blackbird Mountain Guides is in direct contact with the emergency contacts of the affected clients and guides and is providing them with regular updates as verified information becomes available.”

On its website, the company advertises the ski trip to the Frog Lake Huts for those with an intermediate to advanced skill level.

Rescue ski teams join the effort to rescue backcountry skiers after an avalanche in Northern California Tuesday. Nevada County Sheriff’s Office

Skiers spend their days navigating the mountain off-trail through steep terrain with the aid of guides, before returning to the huts for dinner, the company says.

Following the first call for help Tuesday, dozens of first responders approached the scene from multiple directions: ski rescue teams from Boreal Mountain Ski Resort and Tahoe Donner’s Alder Creek Adventure Center were dispatched, along with rescue crews from surrounding counties.

The rescuers approached the scene on skis and snowcats, with snowmobiles on standby, as they battled the harsh weather in the region, where snow was falling at a rate of 3 to 4 inches an hour Tuesday.

As the time ticked by, the survivors were told to “shelter in place as best they can in the conditions,” the sheriff’s office said.

The stranded skiers were communicating with rescuers through emergency beacons – including some with the ability to send text messages, Captain Russell Greene of the Nevada County Sheriff’s Office told CNN affiliate KCRA.

The group crafted a makeshift shelter from a tarp, “doing everything they can to survive,” Greene said.

California Gov. Gavin Newsom’s office said he had been briefed on the developing situation and the state was coordinating an “all‑hands search‑and‑rescue effort with local partners and deploying resources to support the active response.”

The snow slowed overnight, potentially helping rescue conditions, but on-and-off snow showers are expected through Wednesday as authorities brace for another coming storm Thursday that is expected to bring snow to the region.