The Sherpa guides had gone early in the morning to fix ropes for other climbers when the avalanche hit just them below Camp 2 at about 6:30 a.m., Nepal Tourism Ministry official Krishna Lamsal said from the base camp where he is monitoring rescue efforts.
Rescue workers pulled out 12 bodies from under mounds of snow and ice and were searching for the three missing guides, Lamsal said.
Two Sherpas who were injured were taken by helicopter to hospitals in Nepal's capital, Katmandu.
Hundreds of climbers, their guides and support crews have gathered at the base camp to prepare for attempts to scale the 8,850-meter (29,035-foot) mountain early next month when weather conditions become favorable. 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.
Ang Tshering of the Nepal Mountaineering Association said the area where the avalanche hit is nicknamed the "popcorn field" and is just below Camp 2 at 6,400 meters (21,000 feet).
Earlier this year, Nepal announced several steps to better manage the heavy flow of climbers and speed up rescue operations. The steps included the dispatch of officials and security personnel to the base camp at 5,300 meters (17,380 feet), where they will 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 reach the peak.
The worst recorded disaster on Everest had been a snowstorm on May 11, 1996, that caused the deaths of eight climbers. Six Nepalese guides were killed in an avalanche in 1970.
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