Two of the six were taken to a hospital for treatment, the Nevada County Sheriff's Office said.
The sheriff's office said on Tuesday night that 15 skiers were on the trip, not 16 as initially believed.
Search and rescue crews were sent to Frog Lake in the Castle Peak area, northwest of Lake Tahoe, after an emergency call reporting an avalanche and people buried.
A powerful winter storm was moving through California at the time.
Extreme conditions in the northern California mountains slowed the rescue effort.
It took crews several hours to reach the skiers and take them to safety, where they were evaluated by the Truckee Fire Department.
The sheriff's office said it would provide another update on rescue efforts at a news conference Wednesday morning.
The skiers were on the last day of a three-day back-country skiing trek, said Steve Reynaud, a Tahoe National Forest avalanche forecaster with the Sierra Avalanche Center, which had contact with people on the ground in the area.
He said the skiers spent two nights at huts on a trip that required navigating "rugged mountainous terrain" for up to 6km while bringing along all food and supplies.
Nevada County Sheriff Captain Russell Greene said authorities were notified about the avalanche by the ski tour company that led the expedition, Blackbird Mountain Guides, and by emergency beacons the skiers were carrying.
Rescuers made their way cautiously towards the scene of the avalanche because of the danger of more avalanches.
Blackbird Mountain Guides said in a statement on its website that it was co-ordinating with authorities on the rescue operation.
California is being walloped this week by a powerful winter storm bringing treacherous thunderstorms, high winds and heavy snow in mountain areas.
"It's particularly dangerous in the back-country right now just because we're at the height of the storm," said Brandon Schwartz, Tahoe National Forest lead avalanche forecaster at the Sierra Avalanche Center.
The centre issued an avalanche warning for the area in the Central Sierra Nevada, including the Greater Lake Tahoe region, starting early on Tuesday with large slides expected into Wednesday.
The town of Soda Springs, near where the avalanche took place, recorded more than 70cm of snow in 24 hours.
The dangerous conditions were caused by rapidly accumulating snow piling on fragile snow-pack layers coupled with gale-force winds.
The storm wreaked havoc on roads from the Sierra Nevada to Sonoma County, with traffic halted temporarily in a highway due ot spin-outs and crashes.
Several Tahoe ski resorts were fully or partially closed due to the weather.
Resorts along highways have avalanche mitigation programs and were not expected to be at as high of a risk as the back country, where travel in, near or below avalanche terrain was strongly discouraged, the centre said.
