Four people have died and nine others have been injured in an avalanche south-west of Mont Blanc in the French Alps.

The avalanche occurred in the middle of the day on the Armancette glacier, interior minister Gerald Darmanin said on Sunday.

Those caught up in it were backcountry skiing in the mountains, said Emmanuel Coquand, spokesman for the local authorities of Haute-Savoie, adding that they were still confirming the identity of the victims.

He said the avalanche was extensive, covering an area of one kilometre by 500 metres at an altitude of 3500 metres.

The cause is being investigated.

The glacier lies near the village and ski resort of Les Contamines-Montjoie.

President Emmanuel Macron wrote on Twitter that rescue services were continuing to search for further casualties and that his thoughts were with the victims and their families.

– AAP