Skiing conditions had been "good" on Easter Sunday, the mayor of the town of Contamines-Montjoie, Francois Barbier, told AFP.
"I think it's the most deadly avalanche this season."
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, according to the prefecture.
"We're thinking of (the victims) as well as of their families," President Emmanuel Macron wrote on Twitter.
Two brothers died in an avalanche on the same glacier in 2014, both were experienced climbers in their 20s.
