Three German skiers were killed when an avalanche struck above the village of Ayer in the Swiss Alps, the second incident involving tourists in less than a week.

The skiers were part of a group of nine cross country skiers, who were travelling without a guide. According to reports, the party were pulled from the snow after rescuers arrived by helicopter.

The avalanche, at 2,500 metres altitude, was 500 metres wide and 500 metres long.

Weather is the biggest factor that causes avalanches. The risk of avalanches in the region has increased as warm temperatures have begun to melt the snow.

Each year the Alps receive approximately 12% of the world tourists (World Tourism Organization). In 2001 more than 80 million tourists visited the Alps.

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