Global warming is blamed as a huge section of Mont Blanc glacier on the Italian side looks set to break away.
Italian authorities have closed roads and evacuated mountain huts after experts warned that part of a glacier on Mont Blanc could collapse.
About 250,000 cubic metres of ice are in danger of breaking away from the Planpincieux glacier on the Grandes Jorasses peak, officials said.
The mayor of the nearby town of Courmayeur said global warming was changing the mountain.
On Tuesday, Courmayeur Mayor Stefano Miserocchi signed an order closing roads in the Val Ferret on the Italian side of Mont Blanc, after experts warned that a section of the glacier was sliding at speeds of 50-60cm (16-23in) per day.
The Mont Blanc massif is Western Europe’s highest mountain range. It has 11 peaks above 4,000m in France and Italy and attracts hundreds of thousands of tourists every year.