Two climbers in the group were rescued, and emergency crews using dogs and helicopters scoured the churned-up snow Thursday to search for the missing. The avalanche came after unusually wet weather and sent climbers hurtling down steep slopes at the height of the summer climbing season. Police said one of the climbers may have kicked the ice sheet loose.
The dead were from Britain, Germany, Spain and Switzerland, according to the gendarme service in the French mountain town of Chamonix.
A group of 28 climbers from Switzerland, Germany, Spain, France, Denmark and Serbia was believed to be in the expedition caught in the early morning avalanche about 4,000 metres high on the north face of Mont Maudit, part of the Mont Blanc range.
Some climbers managed to turn back in time, regional authorities in Haute-Savoie said.
The gendarme service said they were alerted around 5:25 a.m. local time Thursday to the avalanche. A block of ice 40-centimetres thick broke off and slid down the slope, creating a two-metre-thick, 50-metre-long mass of snow.
Several dozen gendarmes and other rescuers worked to pull the dead and injured from the mountain and search for the missing but the risk of a new avalanche complicated the search.
The 11 injured were hospitalized in nearby Sallanches, the gendarme service said.
It appears that early summer storms left behind heavy snow that combined with high winds to form dangerous avalanche conditions on some of the popular routes around Mont Blanc, the highest mountain in western Europe.
"The first elements that we have from testimony are that a climber could have set loose a sheet of ice, and that sheet then pulled down the group of climbers below. I should say that the incline was very, very steep on this northern face," Col. Bertrand François of the Haute-Savoie gendarme service told reporters.
According to tweets from climbers, high winds led to overhanging ice slabs forming on the slope. Five days ago, they tweeted that Chamonix saw a monsoon-like downpour that turned to snow at 3,000 metres high.
Jonas Moestrup from the western Danish city of Randers heard about the accident when he was on his way down from Mont Blanc.
"Three days ago, we ascended it [Mont Maudit]. It was shocking to hear, it could easily have been us," he told the Danish news agency Ritzau by telephone. "It is scaring and tragic. It is part of the thrill that something can go wrong."
French Interior Minister Manuel Valls was expected to arrive at the site later Thursday.
The German Foreign Ministry said three Germans were killed and Spain confirmed two of the dead were Spanish. The Danish Foreign Ministry said two Danes were involved in the avalanche. One was injured and the other was safe.
Some of the climbers were with professional guides, others were independents. French investigators will examine the circumstances of the deaths.
The Mont Blanc massif is a popular area for climbers, hikers and tourists but a dangerous one, with dozens dying on it each year. Chamonix, a top centre for climbing, hosted the first Winter Olympics in 1924.
Regional authorities had warned climbers earlier this summer to be careful because of an unusually snowy spring.