Nepal's Sherpa community is confronting a dark tragedy after at least 12 guides were killed by an avalanche that swept down a climbing route on Mt Everest. A search was ongoing for at least three more guides still missing following the deadliest ever single day on the world's highest mountain.

Officials said the men were killed after the avalanche struck at around 6.30am on Friday as they were laying fixed ropes for other climbers. Rescue workers struggled to pull their bodies from mounds of snow and ice after they were struck just about Camp 2. Two men, who survived but suffered injuries, were lifted from the ice debris and flown by helicopter to Kathmandu.

A spokesman for Nepal's Tourism Ministry, Mohan Krishna Sapkota, told the AFP news agency that all the climbers involved were of Nepali origin and had been preparing the route ahead of the main spring climbing season, which starts in a matter of days.

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"The sherpa guides were carrying up equipment and other necessities for climbers when the disaster happened," he said.

Friday's deaths easily surpassed the previous highest number of deaths on Everest. That occurred on May 11 1996 when eight foreign climbers were killed in bad weather, an event that featured in journalist Jon Krakauer's book Into Thin Air. Six Nepalese guides died in an avalanche in 1970.

Hundreds of foreign and local climbers have gathered at the base camp of Everest to prepare for attempts on the 29,035-foot mountain early next month when weather conditions become optimal and provide a small, brief window of opportunity for people to realise their ambitions. In preparation, teams of sherpas have been setting up fixed ropes that their clients, who pay many thousands of pounds to scale the peak, will attach themselves to while ascending the mountain.

The avalanche is said to have struck in an area situated at around 21,000ft and known as the "popcorn field". The area lies on the route towards the notorious Khumbu ice fall, an unavoidable passage which has claimed the lives of many climbers over the years.

In recent years the number of climbers in Everest, especially those with less experience, has soared and the Nepalese authorities have introduced measures to try and better organise the flow. Officials have been dispatched to base camp to spend the climbing season there and address any problems

Yet impoverished Nepal is loathe to deter climbers from scaling the peak because of the permit fees they pay and the employment they provide for sherpas and other support members. So far, a total of 334 permits have been issued to foreign climbers for the year, up from 328 last year. There has even been talk of reducing the cose of permits to encourage yet more mountaineers.

Climbers have complained that overcrowding on the mountain, especially at crucial points such as the Hilary step, has led to increasing numbers of unnecessary deaths.

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. Around 250 people have died doing so.

Friday's deaths underscore the perilous work undertaken by the sherpas, who lug ropes, tents and supplies for foreign climbers. It was reported that Kathmandu-based climbing company Himalayan Climbing Guides Nepal had confirmed two of their guides were among the dead and other employees were among those still missing.