The Sherpa guides had gone early in the morning to fix ropes for hundreds of climbers when the avalanche hit them just below Camp 2 about 6:30 a.m., said Nepal Tourism Ministry official Krishna Lamsal, speaking from the base camp where he is monitoring the rescue efforts.
Four bodies have been recovered and rescuers were digging two more out of the snow, he said. Nine more Sherpas are unaccounted for and believed to be buried, he said.
Hundreds of climbers, their guides and support guides had gathered at the base camp, gearing up for attempts to scale the 8,850-meter (29,035-foot) peak early next month when weather conditions become favorable. Ahead of that, they have been setting up camps at higher altitudes and guides have been fixing routes and ropes on the slopes above.
As soon as the avalanche hit, rescuers and fellow climbers rushed to help. A helicopter was also sent from Katmandu.
Ang Tshering of the Nepal Mountaineering Association said that the area where the avalanche hit is nicknamed the ''popcorn field,'' which is just below Camp 2 at 6,400 meters (21,000 feet).
Earlier this year, Nepal announced several steps to better manage the flow of climbers, minimize congestion and speed up rescue operations. Preparations included the dispatch of officials and security personnel to the base camp located at 5,300 meters (17,380 feet), where they would stay throughout the spring climbing season that ends in May.
More than 4,000 climbers have scaled the summit since 1953, when it was first conquered by New Zealander Edmund Hillary and Sherpa Tenzing Norgay. Hundreds have died attempting to climb the mountain.
The worst recorded disaster on Everest was on May 11, 1996, when eight climbers were killed in one day because of a snow storm in areas near the summit. Six Nepalese guides were also killed in an avalanche in 1970.