Six climbers have died and an unknown number of others are missing in an avalanche in Mount Qomolangma, also known as Everest, officials said on Friday.

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

Four bodies have already been recovered and brought at the base camp and a rescue team is looking for the other two.

Continuous snowfall in the world's highest mountain affected the preparations of the climbers last week.

"Nepali Sherpa's were busy to make preparations, including fixing ropes, and died as the avalanche hit them," Ang Tshering Sherpa, president of the Nepal Mountaineering Association, told Xinhua.

Some others are still missing and search and rescue operation is underway, he added.

Officials said the rescue operation has been difficult as there is continuous snowfall.