Nine climbers have been killed in an avalanche near the French Alpine ski resort of Chamonix.
Three of those killed were from the UK, three from Germany, two from Spain and one from Switzerland. Twelve other climbers were reported injured.
Local authorities deployed rescue teams in helicopters and said it was the deadliest avalanche in recent memory.
Police said four others believed to have been missing - two Britons and two Spaniards - had now been accounted for.
The Britons had started out on their climb but turned back, while the Spaniards had chosen a different route, said Emmanuel Vegas, a lieutenant with Chamonix police.
The alarm was sounded at 05:25 local time (03:25 GMT) by one of the injured on the slopes of Mont Maudit.
The route is popular with summer tourists heading for the summit of Mont Blanc.
In all, 28 climbers were roped together in several groups on Thursday morning.
They are believed to have reached 4,000m (13,120 ft) when the avalanche struck.
Chamonix mayor Jean-Louis Verdier told Reuters news agency the avalanche was completely unexpected.
"We had no more reason than usual to be alarmed," he said.
"It's a steep mountain face. There are big plates of snow where an avalanche can easily occur. But this morning we had no reason to expect an avalanche of this size and such a tragedy."
The French authorities described the avalanche as "the most deadly" in recent years.
Chamonix-based mountain guide Richard Mansfield described the area as "very beautiful", but said that it was avalanche-prone.
He said the slopes on Mont Maudit faced away from the prevailing wind, which meant snow could be pushed over forming slabs.
"These can easily be set off by a passing climber, causing an avalanche," he said.
Visiting the area, Interior Minister Manuel Valls described the incident as "catastrophic" and said a full investigation was under way.
British Foreign Secretary William Hague said he was "very saddened" by the tragedy and thanked the French rescue services for their efforts.
"We are in very close contact with the French authorities and our ambassador and consular officials are heading to Chamonix to provide consular assistance. We will offer whatever support and assistance we can," he said in a statement.
The UK Foreign Office later confirmed that one of the British climbers killed in the Alps was Roger Payne, a former chief executive of the British Mountaineering Council (BMC) and president of the British Mountain Guides.
Mont Maudit - meaning the "cursed mountain" - is the third-highest peak in the Mont Blanc massif range, rising to 4,465m.
Eight climbers were killed in an avalanche near Mont Maudit in 2008.