The Nevada County Sheriff’s Office reported that highly trained ski rescue teams from nearby resorts were deployed immediately. The six survivors have been instructed to take shelter while waiting for rescue amid severe winter storm conditions and zero visibility.

Captain Russell Greene of the sheriff’s office warned that the operation would be slow and careful due to ongoing avalanche risks. Around 46 rescuers were en route Tuesday night, but harsh weather had slowed access to the site.

The group involved included 12 clients and four ski guides. Survivors have remained in contact with rescue teams via messaging and radio and have set up makeshift shelters.

Avalanche-related incidents are common in the US, with an average of 12 fatalities each winter over the past decade. The Sierra Avalanche Center had issued a “high avalanche danger” warning shortly before the tragedy.

If the missing skiers are not found, this incident could become one of the deadliest avalanches on record in the United States