(CNN) -- A summer climbing expedition in the French Alps turned to tragedy Thursday when a six-foot-thick wall of snow came crashing down on two groups of climbers, leaving at least nine dead, French police said.
Two people caught in the avalanche were found alive in the snow afterward, but at least four people remained missing, and French police said. Nine people were taken to a hospital with slight injuries.
The dead climbers include people from Germany, Britain, Spain and Switzerland, police said.
The nationalities of the missing are unknown, police said. There were also French climbers in the party.
Two groups of climbers were caught in the avalanche on the north side of Mont Maudit in the Mont Blanc range, near Chamonix on the French-Italian border, police said.
A total of 28 climbers in the two groups were connected by ropes, authorities in Annecy, France, said.
A mountain rescue unit was called out at 5:25 a.m. after the avalanche was triggered when a sheet of ice dislodged.
Some of the climbers managed to get themselves back to their base at the Refuge des Cosmiques.
The rescue operation is continuing, police said.
French Interior Minister Manuel Valls is to visit Chamonix on Thursday afternoon to see the rescue efforts, the Interior Ministry said in a written statement.
He was greatly saddened by the news and expressed profound sympathy and support for the victims and their families, the statement said.
Valls also paid tribute to the efforts of local police and rescue workers as they continued the search for any survivors trapped under the snow.
French newspaper Le Figaro quoted a Chamonix official as saying weather conditions had been good on Thursday morning, giving the climbers no clue that a deadly avalanche might be unleashed.
The route they took up Mont Maudit is often used by climbers tackling the mighty Mont Blanc, the newspaper said.