A teacher led a school group on to a slope in the French Alps that had been closed because of the risk of avalanches, an official says.

An avalanche killed at least three people and seriously injured others when it swept into the skiers, including the group of schoolchildren.

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The dead were two teenagers, aged 14 and 16, and a Ukrainian adult skier who was not with the school group, according to police and an official from the Les Deux Alpes resort, which is about 50km from the Italian border.

A teacher had led the group on to the black-rated slope, regional state government official Jean-Paul Bonnetain said on Wednesday.

Three teenagers suffered cardiac arrest while the teacher was also seriously injured, Bonnetain told journalists.

Apart from the two teenagers who died, all other students from the group of 19 had been accounted for and were safe, the ministry said.

Rescue teams worked into the evening searching for other skiers who may have been buried in the snow.

The avalanche happened in late afternoon, after a large sheet of snow broke off above the slope following several days of heavy snowfall.