The Himalayan Trust has launched an appeal to help the families of the Sherpa climbers killed in a devastating avalanche on Mt Everest.

At least 12 Nepalese advance party guides were killed and four others were missing after the avalanche struck about 6.45am local time (12.45pm NZT) on Friday in an area known as "popcorn field", just above Everest base camp at 5800m.

The members of the Himalayan Trust, like many around the world, were devastated and appalled by the news, trust chairman Mike Gill said.

The incident is the deadliest accident on the world's highest mountain.

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Three seriously injured climbers had been rescued from the mountain and were receiving medical treatment in Kathmandu.

"We extend our heartfelt condolences to the families and friends of the climbers," Mr Gill said.

"Many of the climbers are from the upper Khumbu area, where we focus our development aid.

"The tragedy is a reminder that while Everest has increased in popularity and accessibility over the last 60 years, Nepalis have continued to bear much of the risk involved in summiting."

The Himalayan Trust had launched a fundraising appeal to help the families impacted by the tragedy, Mr Gill said.

Funds raised will provide education scholarships to the children covering educational and living expenses - ensuring they have a guaranteed schooling despite the loss of their fathers' livelihoods.

Four New Zealanders were among a climbing group on the mountain when the avalanche struck.

The two women and two men were with a team from Wanaka-based company Adventure Consultants which organises trips to the world's highest summit. Three of the dead Sherpas, who lived in Nepal, were also working for the firm.

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Expedition leader Dean Staples, base camp manager Caroline Blaikie, food boss Sarah Macnab and electrician Mark Ayre were a six-hour hike from the disaster when it hit.

Adventure Consultants general manager Suze Kelly said the staff, all based in Wanaka, were in shock at the base camp and watching helplessly as helicopters ferried dead colleagues off the mountain.

"We have been in constant contact with our team by satellite phone and a big priority was letting their families back here know they are safe," Ms Kelly said.

"The climbing fraternity is a close-knit community and everyone is devastated by what has happened. "The Sherpas were carrying supplies and food from the base camp to another spot further ahead when they encountered the avalanche.

"We are relieved that our team at base camp are safe but saddened by the death of the Sherpas, who we had employed for the trip."

Expedition leader Staples, 49, has summited Everest nine times. The experienced New Zealand team set off with 25 contracted Sherpas on the first stage of the climb on April 2.

"The team is still at the base camp and at this stage we do not know when they are expected to return," Ms Kelly said. "They have not had much sleep and are now pretty exhausted. Losing their Sherpa friends has been the hardest part. It is a lot to take in."

A Nepalese Sherpa Dawa Tashi, who was injured during an avalanche, gets treatment at a hospital in Katmandu, Nepal. Photo / AP
A Nepalese Sherpa Dawa Tashi, who was injured during an avalanche, gets treatment at a hospital in Katmandu, Nepal. Photo / AP

Ms Kelly said Adventure Consultants had been operating for more than 20 years and chief executive Guy Cotter was on his way from New Zealand to Nepal to help.

The three dead Sherpas who were working for the Wanaka firm are: Phurba Ongyal from Pangboche, Lakpa Tenjing from Khumjung and Chhring Ongchu from Khumjung.

Kiwiblog author David Farrar, from Wellington, was returning from a trek to Everest Base Camp with a party of New Zealanders when the disaster happened. "We were in the Base Camp area two days before the avalanche," he told the Herald on Sunday. "The avalanche was up near Camp 1 which is higher up the mountain."

It's understood five of 13 Sherpas killed were employed by an NBC Everest expedition.

Donations to the Everest Avalanche Appeal can be made here.

There was also a Gala Dinner planned at the Auckland Museum and functions in Christchurch and Nelson next month, which would apportion funds raised to the appeal. Details available on the Himalayan Trust website.