Rescue crews are searching for nine missing skiers after an avalanche swept through the Castle Peak area near Lake Tahoe late Tuesday morning. 

The Nevada County Sheriff’s Office says the group of 15 backcountry skiers had been returning from a day-long outing when the slide hit around 11:30 am, triggering a large-scale emergency response. Rescuers battled harsh weather for hours before locating six members of the group and bringing them to safety.

The remaining nine are still unaccounted for as 46 first responders continue combing the snow-covered terrain under dangerous conditions.

Authorities say an avalanche warning had been issued early Tuesday morning, covering the same area for a 24-hour period. The group, made up of 11 clients and four guides from Blackbird Mountain Guides, had been on a three-day trip based at the Frog Lake Backcountry Huts and were heading back to the trailhead when the avalanche struck.

Blackbird Mountain Guides says it is working closely with the Nevada County Sheriff’s Office and search and rescue teams as the operation continues.