In the wee hours of Thursday morning ice from a high cliff on Mont Maudit fell on a group of 28 mountaineers of different nationalities.

The incident set off an avalanche 150 metres wide that swept away those in its wake. Within seconds three British, two Swiss, two German and two Spanish climbers lost their lives.

The accident took place on a long glaciated slope from Mont Blanc du Tacul up to the summit of Mont Maudit. A spokesman for the Alpine mountain rescue service, which scrambled a helicopter and sniffer dogs to the area after being alerted by an injured climber, told The Guardian that the incident had probably been caused by snow collapsing in the warm July weather.

Chamonix-based mountain guide Richard Mansfield told The Guardian that the route where the accident happened was the second most popular to the top of Mont Blanc.

"It's very beautiful and a common route, but it can have very serious consequences, particularly due to avalanches," he said. 

One of the first persons to reach the scene was British climber and guide Victor Saunders and his client, a doctor. They gave first aid to the survivors and called the rescue services.

Saunders and the doctor helped recover bodies, treat the injured and help the rescue services load them aboard helicopters.

When Saunders reached Mont Blanc du Tacul, he figured something was definitely wrong.

The 4,465-metre Mont Maudit is widely considered one of the world's most dangerous climbs. The dead climbers were believed to have reached an altitude of around 4,000 metres when they were swept away.

There have been several deaths in the Alps this summer. This month five German climbers fell to their deaths in a single incident in Switzerland.

The French interior minister, Manuel Valls said, "My thoughts are with those victims, with the British and Spanish and German victims, Swiss victims, and my thoughts are with their families who have discovered this painful tragedy. It is a personal one. We have seen many accidents on the Mont Blanc Mountain but we should note that the number of victims and those who have disappeared and the injured is very high. This accident is catastrophic."

"I am very saddened by the tragedy in Chamonix, and I send my deepest condolences to the friends and families of those affected," British foreign secretary, William Hague, told reporters. "We are in very close contact with the French authorities and our ambassador and consular officials are heading to Chamonix to provide consular assistance."