An avalanche swept over a group of European climbers in the French Alps, killing nine people on the slopes of a peak dubbed the "Cursed Mountain".
Although four climbers were first reported missing, police later said they were alive and accounted for, with two of them having cancelled their climb and two having taken a route different to the deadly one.
The nine people known to have died in the early Thursday avalanche on Mont Maudit ("Cursed Mountain" in French) were three Britons, three Germans, two Spaniards and a Swiss, said local police Colonel Bertrand Francois.
Nine more climbers were lightly injured and treated at a local hospital.
Among the dead was a British mountain guide, the French PGHM mountain rescue group said, and a French guide was among the injured.
British Foreign Secretary William Hague said he was "very saddened" by the tragedy and was sending "deepest condolences to the friends and families of those affected."
One of the injured sounded the alert at around 0325 GMT after the avalanche on Mont Maudit, the massif's third-highest peak.
It rises to 4,465 metres (14,650 feet) and is considered one of the more difficult paths to the summit of Mont Blanc that at 4,810 metres (15,781 feet) is western Europe's highest peak.
The avalanche was thought to have been triggered when a climber caused a sheet of snow and ice to break off the mountainside.
Officials said the victims had been in a group of more than 20 people, including guides, who had left a base at 3,600 metres at around 1:30 am local time (2330 GMT Wednesday) for the climb.
Among those killed was the former general secretary of the British Mountaineering Council, Roger Payne, the organisation said, expressing its condolences to his family.
Its chief executive Dave Turnbull said: "Roger was one of the UK's most enthusiastic and respected climbers with a track record of Alpine and Himalayan mountaineering stretching back to the 1980s."
Originally the police thought that four more climbers were missing after the disaster, based on the guest list of a mountain refuge from which the alpinists had started out on their ascent.
But later on, Thursday Emmanuel Vegas, a lieutenant with Chamonix police, told AFP that the two Britons thought missing had taken a route different to the one hit by the slide, and the two Spaniards thought missing had resold their spots in the refuge to two of the climbers who were killed.
About 50 rescuers, including from Italy, had joined the search at a height of more than 4,000 metres (13,100 feet), where snow drifts in some cases were up to six metres (20 feet) thick.
Delfino Viglione, local director of mountain rescue for the border patrol police, told AFP that climbing in the famed area is difficult.
"It is a tough, steep part of the mountain. The wind probably led to an accumulation of snow that dislodged when the climbers passed," he said.
"Mont Blanc can be problematic even in the summer. You should never lower your guard. Unfortunately these tragedies happen often."
Thursday's accident marked the deadliest climbing disaster in France since August 2008, when eight climbers -- four Germans, three Swiss and an Austrian guide -- were swept away after blocks of ice broke off Mont Blanc du Tacul, prompting an avalanche.
Some 20,000 climbers attempt to reach the summit of Mont Blanc every summer, with up to a 500 a day during peak times.
Experts said the increasing number of climbers was boosting risks.
"The increased use is a danger in and of itself because it slows down the rope parties," said Philippe Descamps, the secretary general of the Petzl Foundation, which promotes mountain safety and the environment.
Increased numbers also give climbers a false sense of security, he said.
"Because we are many, we are much less careful," he said, adding that increased numbers "give a sense of security and can reduce alertness."
Denis Crabieres, the head of France's National Union of Mountain Guides, also said increased traffic heightened risks on the mountainside.
"A significant number of people in the same area causes behaviour that we wouldn't see otherwise," he said.
"This can make rope parties pass each other in unsuitable terrain. It's a bit like when there a lot of people on the road," Crabieres said.