Eight skiers have been killed and one remains missing following an avalanche on Tuesday in Nevada County, U.S. Northern California, local authorities said Wednesday.

Nevada County Sheriff Shannan Moon said at a news conference that the avalanche struck a group of backcountry skiers in the Sierra Nevada mountains, making it the deadliest avalanche in the country in more than four decades.

Moon told reporters that authorities had informed the families of those involved that the operation had officially shifted from rescue to recovery.

Eight bodies have been located, and crews were working to transport the remains off the mountain for autopsies to determine the cause of death, authorities said.

Six survivors were rescued Tuesday evening after search and rescue teams navigated blizzard conditions for several hours, the sheriff's office said, adding that two of the six were taken to a hospital for treatment with no life-threatening injuries.