Rescue crews on skis and snowcats battled dangerous, blizzard conditions on Tuesday in an effort to reach six backcountry skiers trapped after an avalanche high in the rugged Northern California mountains that left 10 other skiers missing.

The search and rescue crews were dispatched to Frog Lake in the Castle Peak area, northwest of Lake Tahoe, after someone called 911 at about 11:30 a.m. local time to report an avalanche with people buried as a powerful winter storm moved through the state.

Hours later, Ashley Quadros, a spokesperson with the Nevada County Sheriff’s Office, said six skiers had been located and were asked to shelter in place “as best they can” until they can be reached.

The group was on the last day of a three-day backcountry skiing trip, said Steve Reynaud, a Tahoe National Forest avalanche forecaster with the Sierra Avalanche Centre.