The most deadly avalanche in the Alps since 2008 swept down a popular climbing route in the Mont Blanc range near the border with Switzerland at about 0300 GMT.
The dead included two Spaniards, three Germans, one Swiss and three people whose nationalities had not yet been ascertained, the head of the Haute-Savoie rescue squad, Bertrand Francois, told a press conference.
Two German and two British climbers were still missing and nine other people were injured.
About 38 climbers were on the mountain - one of two access points to the famous Mont Blanc peak - at an elevation of about 4,000 metres (13,000 feet) when the avalanche hit without warning in fine weather conditions, Francois said.
That included 28 climbers in two separate climbing teams, as well as solitary climbers, he added.
Authorities had not expected avalanches, as conditions were good on Thursday morning, said Jean-Louis Verdier, mayor of the resort town of Chamonix.
"We had no more reason than usual to be alarmed," Verdier told Reuters TV. "It's a steep mountain face. There are big plates of snow we know of where an avalanche can easily occur. But this morning we had no reason to expect an avalanche of this size and such a tragedy."
A preliminary investigation suggested a climber may have stepped on an icy patch and set off the slide.
One of the climbers who managed to escape alerted authorities.
Rescue workers in helicopters and on foot, as well as dog teams, were searching on Tuesday afternoon for the missing.
Eight Swiss, German and Austrian climbers perished in an avalanche nearby in 2008.
France's interior minister was expected in the area later on Thursday.