The heavy snowfall has added difficulty to the search for nine Nepali Sherpa climbers who are still missing when an avalanche hit their base camp on Mount Qomalangma, also known as Everest, early Friday.

The avalanche also left six climbers dead.

"We have demanded two heliometers to search and rescue the missing climbers but due to the heavy snowfall, the task has been affected," Lama Kaji Sherpa, general secretary of the rescue committee, told Xinhua over the telephone.

The avalanche hit the area just below Base Camp 2 at about 6.30 a.m. local time Friday, said Madhu Sudan Burlakoti, joint secretary from the Ministry of Culture, Tourism and Civil Aviation.

Most of the climbers who died are Nepali Sherpas who were there to make technical preparations for the climbing season beginning next week.

The local Sherpas are renowned in the international climbing community for their experience at very high altitude making them expert guides and porters for foreign mountaineers.

Hundreds of climbers and their guides have gathered at the base camp, getting acclimatized before climbing the world's highest peak early next month.

Officials from Nepal's Ministry of Culture, Tourism and Civil Aviation said at least 334 permits for Mount Qomolangma have been issued, compared with 329 issued at the opening of the spring climbing season last year.

More permits are expected to be handed out in the coming days.