Rescuers pulled six survivors from a remote California mountainside after a large avalanche swept through a backcountry skiing group near Castle Peak, northwest of Lake Tahoe, authorities said Tuesday night.

The Nevada County Sheriff’s Office said 15 skiers were caught in the slide. Six people were located alive and rescued after teams spent hours navigating dangerous terrain and harsh conditions to reach them. Two of the survivors were transported to a hospital for treatment.

Nine others remained missing as of late Tuesday, and officials said the search was continuing but could be affected by weather.

Captain Russell Greene of the sheriff’s office said the avalanche was first reported around 11:30 a.m. by a mountain guide service. The incident was also separately reported through an emergency beacon device, helping alert rescuers to the location.

By Tuesday evening, roughly 46 rescuers were moving toward the site, Greene said, as emergency teams worked against time, terrain, and worsening conditions.

In a statement released Tuesday night, Blackbird Mountain Guides said the group involved included both clients and guides. The company said the skiers were returning to the trailhead at the end of a three-day trip when the avalanche occurred.

The group had been staying at Frog Lake Backcountry Huts since Sunday, the company said. The huts are located in a high alpine setting near an alpine lake, in an area known for popular winter backcountry routes.

Authorities said the rescue effort was ongoing, and updates would depend on conditions and access to the site.