Among the dead were two mountain guides caught by the snow tumbling down the Armancette glacier, the prefecture for the Haute-Savoie department said on Sunday.
Investigators have been called in to help with the search for the person still unaccounted for in the Alps.
One person also suffered slight injuries in the avalanche while eight others also swept up were unharmed, the prefecture said. The avalanche covered an area of 1,000 metres by 500 metres.
No avalanche warning had been issued for the region by weather authority Meteo France, but a combination of warmth and wind may have been behind the disaster, the prefecture added.
"We're thinking of [the victims] as well as of their families," President Emmanuel Macron wrote on Twitter. "Our emergency services have been mobilised to find those still trapped in the snow."
Emergency responders had deployed a helicopter as well as mountain rescue dogs to the scene, although the prefecture warned that a further avalanche could not be ruled out.
The operation was suspended in the evening, but will resume at 7am (0500 GMT) on Monday.
"I think it's the most deadly avalanche this season," Contamines-Montjoie's mayor, Francois Barbier, told AFP.
Two brothers, both experienced climbers in their 20s, died in an avalanche on the same glacier in 2014.
Source: Agence France-Presse
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