"There was an attempt at a helicopter overflight (Tuesday) morning... but the rescuers couldn't get through the cloud barrier and turned back," the prefecture in the Haute-Savoie department told AFP.

A second helicopter was set to lift off in the afternoon when the weather is forecast to clear, in search of the two South Koreans and two Italians, the authority added.

Meanwhile a group of Italian mountain rescuers had set off on the ground on Tuesday morning, the prefecture said.

"It's very possible to survive longer than three days if you can protect yourself from the wind and the cold," a senior officer in Chamonix' PGHM mountain police said.

Police were alerted late Saturday about "three missing climbing parties near the summit of Mont Blanc in very poor weather conditions".

An intensive rescue effort retrieved two Koreans at 4,100 metres (13,450 feet) on Sunday morning.

But the weather has worsened since, leaving rescuers unable to keep up the search for the two Italians and two Koreans still out on the mountain.

One senior PHGM commander told regional daily Le Dauphine Libere that they had briefly reached the Italians by phone and gleaned their location 4,600 metres up on Mont Blanc's north face, but that the connection had cut out.

At 4,809 metres, Mont Blanc is western Europe's highest peak and very popular with climbers from all over the world.