The tragedy on the world's highest peak occurred after an avalanche swept down a climbing route on the 29,000ft mountain.
The Sherpa guides had gone out to fix ropes for other climbers when the avalanche hit them at about 6.30am local time.
It was the highest death toll in a single incident on its slopes since eight climbers died in 1996. An injured survivor told his relatives that the path up the mountain was unstable just before the avalanche. As soon as the avalanche hit, rescuers and climbers rushed to help.
Rescue workers pulled 12 bodies from under mounds of snow and ice and were searching for the four missing guides, Nepal Tourism Ministry official Krishna Lamsal said.
Officials had earlier said three were missing.
The avalanche hit an area nicknamed the "popcorn field" for its bulging chunks of ice which is just below Camp 2, Ang Tshering of the Nepal Mountaineering Association said.
Camp 2 sits at an elevation of 21,000ft on the 29,035ft mountain.
Survivor Dawa Tashi was airlifted to the Grande Hospital in Kathmandu, where he was in intensive care. Doctors said he had suffered several broken ribs and would be in hospital for a few days.
Mr Tashi told visiting relatives that the Sherpa guides woke up early and were on their way to fix ropes to the higher camps but were delayed because of the unsteady path.
Suddenly the avalanche fell on the group and buried many of them, said his sister-in-law, Dawa Yanju.
Hundreds of climbers, guides and support crews are at Everest's base camp preparing to climb to the summit when weather conditions will be at their most favourable early next month. They have been setting up camps at higher altitudes, and guides have been fixing routes and ropes on the slopes above.
The Sherpa people are one of the main ethnic groups in Nepal's alpine region, and many make their living as climbing guides on Everest and other Himalayan peaks.
More than 4000 climbers have reached the summit of Everest since 1953, when it was first conquered by New Zealander Edmund Hillary and Sherpa Tenzing Norgay.
The previous worst recorded disaster on Everest was a snowstorm on May 11 1996 which caused the deaths of eight climbers. Six Nepalese guides were killed in an avalanche in 1970.
Earlier this year, Nepal announced several steps to better manage the heavy flow of climbers and speed up rescues. The steps included the dispatch of officials and security personnel to the base camp at 17,380ft, where they will stay throughout the climbing season that ends in May.
In all, nearly 250 people have died on the mountain.
Everest is on the border between Nepal and the Chinese region of Tibet and can be climbed from both sides.
Nepal's Tourism Ministry has issued permits to 334 foreign climbers to scale Mount Everest this season, up from 328 for the whole of last year. Nepal plans to cut fees to climb the mountain despite concern about overcrowding.