Kathmandu: An avalanche swept down a slope of Mount Everest on Friday, killing nine Nepali mountaineering guides at the beginning of the main climbing season, a Tourism Ministry official said.

The avalanche hit the most popular route to the mountain's peak and three Nepali guides were injured and some people may be missing, Tilak Ram Pandey, an official at the ministry's mountaineering department, told Reuters.

It was the first major avalanche on Mount Everest this climbing season, when hundreds of foreign and Nepali climbers flock to the mountain to attempt to climb its 8,850 metre (29,035 feet) peak.

The avalanche hit the sherpa guides between base camp and camp 1 early on Friday, Pandey said.

Madhusudan Burlakoti, a senior official at the ministry, said helicopters and rescuers on foot had been sent to the site.

More than 4,000 climbers have scaled Everest's summit since it was first climbed by Sir Edmund Hillary and Tenzing Norgay Sherpa in 1953. Nearly 250 people have died on the mountain.

Nepal is home to eight of the world's 14 highest peaks.

Everest is on the border between Nepal and the Chinese region of Tibet and can be climbed from both sides.

The climbing season usually ends in late May when rainy season wind and cloud pushes up from the south to cloak the Himalayas.