© AP Photo/Peter KlaunzerTheo Maurer, chief instructor of Alpine Rescue Switzerland, left, talks on his mobile phone as a rescue helicopter of the Swiss emergency service Rega prepares for takeoff from the Diemtig Valley, in the Bernese Oberland, Switzerland.
Avalanches killed five people in the Swiss Alps over the weekend, and bad weather prevented rescuers from reaching three skiers who apparently remained trapped under the snow on Monday, officials said.

Two of the avalanches occurred in central Switzerland on Sunday, the first hitting a group of skiers, the second the rescuers who came to their aid. A third avalanche buried two skiers in southern Switzerland.

Bad weather conditions meant rescuers had to call off foot and helicopter searches in central Switzerland on Monday for two Swiss and a German missing in the Diemtig Valley, 25 miles (40 kilometers) south of the capital, Bern, said regional police chief Otto von Almen.

"According to current information these persons must still be under the avalanche," he told a news conference broadcast on Swiss television SF Info. Officials hold out little hope that the three are still alive.

Three of the dead there - two Swiss and a German - have been identified, von Almen said. A fourth victim who was pulled from the snow alive, but later died from injuries in the hospital, hasn't been formally identified, he said.

Officials are examining what triggered the two avalanches. One rescuer said the first may have been caused by skiers failing to keep a safe distance from each other on a steep slope. The second could have been triggered by the noise of rescue helicopters, said Bernhard Scherz, an official with the Rubigen ski club.

"The cause and development of this tragic accident are the subject of an ongoing investigation," said police chief von Almen.

Officials said the disaster occurred shortly before midday Sunday when a group of eight people skiing off-piste in the Chummli area of the Diemtig Valley was hit by an avalanche that buried two of them.

Rescuers including 27 members of the Rubigen ski club who arrived to help the skiers were hit by a second avalanche at the same spot about half an hour later, police said. Officials subsequently launched a massive operation involving eight helicopters and 100 rescuers in an attempt to save their colleagues and the missing skiers using radar equipment, avalanche poles and sniffers dogs.

Five people were injured and are recovering in hospital, said von Almen. They are a Canadian woman, three Germans and a Swiss national, he said.

An official at the British Embassy, citing information provided by cantonal police, denied initial reports that a British citizen had been injured. The official spoke on condition of anonymity because she wasn't authorized to make public statements.

Separately, two skiers were buried in an avalanche Sunday near the town of Verbier close to Switzerland's borders with France and Italy. A Swiss man was killed, police in the southern canton of Valais said. His guide was rescued alive.

The start of the ski season and heavy snowfall in recent days have prompted officials to warn of a heightened avalanche risk in the Swiss Alps.