At least eight skiers were killed in a massive avalanche in California’s Lake Tahoe backcountry, authorities confirmed on Wednesday. The avalanche struck the Castle Peak area, northwest of Lake Tahoe, around 11:30 a.m. local time on Tuesday. Six people were rescued alive, while one person remains missing and is presumed dead. The avalanche was described by witnesses as roughly the size of a football field.

Following a 911 call received at 11:30 a.m., the Nevada County Sheriff’s Office launched a search and rescue operation. The sheriff’s department, its search and rescue team, and the California Department of Forestry and Fire Protection jointly conducted the operation in the affected area. Officials said the search continued in the Castle Peak zone immediately after the avalanche.

Authorities have not yet released the identities of the victims or the cause of the avalanche. Search efforts are ongoing for the missing skier.