The avalanche struck around 06:45 local time in an area known as the “popcorn field”, just above Everest base camp at an elevation of 19,000ft.
An official said four bodies had been found and two more were being dug out of the snow.
Everest is crowded ahead of peak season on the 8,850 m summit.
The Sherpa guides had climbed up the slope early in the morning to fix ropes for climbers and prepare the route for mountaineers when the avalanche hit, officials are quoted as saying by the Associated Press news agency.
A number of others are thought to be missing.
More than 3,000 people have scaled Mount Everest since it was first conquered by Edmund Hillary and Tenzing Norgay in 1953, but many have died in the attempt too.
Straddling Nepal and China, the world’s highest mountain has an altitude of 29,029ft (8,848 m).
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