It wasn't the start to Everest's diamond jubilee the Nepalese government had wanted. Sixty years ago, on 29 May 1953, Sir Edmund Hillary stood with Tenzing Norgay on the summit of the world, a symbol of human co-operation. On Saturday, three of the world's leading mountaineers fled the mountain in fear of their lives as an angry mob of Sherpas reportedly threatened to kill them.

The three climbers – Ueli Steck from Switzerland, Italy's Simone Moro and British alpinist Jon Griffith – had been moving without ropes more than 7,000m (23,000ft) up the mountain's Lhotse face, which leads to the South Col, acclimatising for a later attempt on a new route.

At the same time, a team of Sherpas was fixing ropes for guided climbers to use on their way to the summit later in May when the weather is best for climbing. As the trio crossed these ropes on their way towards their tent at camp 3, there was a heated exchange. The Sherpas claim one of them was struck by ice dislodged by one of the three westerners, an allegation that is hotly denied.

Later, when the climbers returned to camp 2, a much larger group of Sherpas attacked the three men – Moro and his companions claim 100, other witnesses say a few dozen – punching and kicking them and throwing rocks, and one, according to Steck, waving a pocket knife. Moro claimed they were told that "by that night one of them would be dead and the other two they would see to later".

Other foreign climbers intervened and after an hour the situation had calmed enough for the three men to flee camp 2 and return to base camp. Moro says they chose another, more dangerous route from that normally used to avoid meeting anyone on the way down. Steck says he is now considering whether to abandon his expedition because of fears for his safety – not from the mountain but from Sherpas working there.

In a message posted from base camp on his Facebook page, Griffith said: "We only lived thanks to some very brave people; we felt for sure that we were going to get stoned to death. I would like to think that anyone who has climbed with us knows that we are more than capable and would never interfere with the Sherpas' work."

Many climbers are familiar with the tensions that can be prompted by sharing a route on a dangerous mountain. Robust exchanges can happen, exacerbated by differences in language and culture. But it is unprecedented for a large group of Sherpas to attack foreign climbers. Liz Hawley, who has tracked Nepalese climbing since the 1960s, said she had "not heard of any such incident before".

Three Sherpas believed to be at the centre of the attack have been ordered off the mountain and are currently helping Nepalese police with their enquiries.

What has so surprised the international climbing community is the target for the Sherpas' wrath. Steck, nicknamed the Swiss Machine, has made a speciality of climbing difficult alpine routes without ropes in record times and now does the same in the Himalayas. He is widely respected for his views on how climbing should be practised.

Moro has climbed Everest four times and made the first ascent in winter of Makalu, the world's fifth-highest peak. He is also a helicopter pilot, volunteering to fly rescue missions in Nepal. He was awarded a fair play award by Unesco for the rescue of a British climber in 2001.

Griffith, one of Britain's most capable alpinists as well as a leading climbing photographer, said: "The reasons behind the attack are complicated and to do with the relationship between westerners and Nepalis on the mountain over many years – not because of our direct actions."

Since Hillary's era, Everest has become an important source of tourism revenue for Nepal. Tens of millions of dollars are now spent along the trail to Everest base camp. On the mountain itself, Sherpas who once worked entirely under the direction of western guides, carrying loads for less capable clients, are now taking responsibility for more of the services required to bring tourists to the summit, including the fixing of ropes.

But if Sherpas have gained materially from the growing numbers of people tackling Everest, as a group they have suffered by far the largest number of fatalities. This year, Mingmar Sherpa, one of the so-called "icefall doctors" fixing and maintaining ropes through the glacier at the foot of the peak, was killed when he fell into a crevasse between camps 1 and 2.

That followed the death in January of Ang Nima Sherpa from the nearby village of Pangboche. The 59-year-old was the leader of the icefall doctors for many years, and responsible for increasing Sherpa influence in how the mountain is managed. Nepal was recently admitted to the International Federation of Mountain Guides Association – a mark of improving standards among Sherpa climbers.

Tension remains between tourism authorities in Kathmandu that collect the $10,000 (£6,450) fee to climb Everest, the local Sherpa population who live at the foot of the mountain and western guides who attract clients on the strength of their reputation for safety.

Climbers of the calibre of Steck and Moro are only a tiny proportion of those on Everest in the modern era. One Everest guide told the Guardian that the sight of three westerners managing without ropes would have antagonised Sherpa guides hard at work.

Despite the jubilee, the number of climbers on Everest this season has fallen slightly from last year and Nepalese tourism authorities were quick to downplay the incident as a "slight misunderstanding".