For generations, traders and their colourful herds of mules and yaks were a lifeline for remote communities in the heart of Nepal's formidable and often dangerous Himalayas.

The traders bravely plied an ancient trail, ferrying salt, grains and other goods between neighbouring China's vast Tibetan plateau and Nepal's middle hills, a profession that endured for centuries.

But the Nepal government's plan to build a road through the isolated border region means the traders' livelihood and their traditional way of life will almost certainly be lost.

The road will allow cars and trucks for the first time to transport goods that have been borne almost exclusively by the traders' teams of animals known as caravans.

"We don't go where there are roads, only to places which have no road access. We can't even begin to compete with trucks," trader Rachhe Kami told AFP as he loaded up his mules in Simikot town, some 3,000 metres (9,840 feet) above sea level.

"When the road is built, I am going to have a big problem. No work will come my way," he said of selling his goods to communities in Humla and neighbouring districts, in Nepal's top northwest corner.

Not everyone despairs of the new road. Many of Humla's 50,000-odd residents living high in the Himalayas hope tonnes of currently scarce goods will soon be quickly and cheaply delivered.

During trading season, lasting roughly from March until November, when the weather is good, Kami spends every night outdoors on the trail. Herders sleep in shifts, taking turns to tend a fire and watch out for snow leopards, wolves and other predators.

The profession, highlighted in the 1999 Oscar-nominated film "Himalaya", is risky.

One of Kami's colleagues fell into a river and drowned last year and the 38-year-old nearly lost his own life when he was caught in a snowstorm near the Nepal-China border in 2012.

"I thought then that I should do something else for a living but this is the only work I can do," the father of four said.

Many traders struggle to make a decent living in this impoverished corner of the world, with communities now sourcing some goods from neighbouring India and elsewhere.

But 50 years ago, business was brisk, profits were high and the animals decked in bells and colourful bridles ruled the snow-capped mountains.

- 'Life force' -

"The caravans used to be the life force of this region -- supplying every household with rice, grains, salt, whatever they needed," 67-year-old Tondhup Lama told AFP.

Lama was a teenager when he followed his father and grandfather into the business, bartering locally-grown barley for Tibetan salt, which he would then trade for rice from Nepal's middle hills.

The fortnight-long journey to the border revealed a world untouched by modernity.

"There was nothing there - we would negotiate with Tibetan nomads living in tents, who would bring us salt and wool which we would barter for grain," he said.

"Back then, we were the rich ones."

The business suffered its first serious setback when Nepal introduced subsidised supplies of iodised salt from India in 1973, aiming to curb illnesses such as goitre and cretinism.

The market for Tibetan salt took a hit but traders adapted quickly, sourcing cheap clothing from India, which they would sell for cash within Nepal or barter for wool and butter at the China border.

In a good month, Lama's family earned up to 20,000 rupees ($201) -- enough to keep them going during harsh winters when heavy snowfall blocks key mountain passes.

"It was a challenging life but I enjoyed the adventure, the travel," he said.

Less than a decade later, the Nepal government dealt another blow and this time business would not bounce back.

New rules designed to protect forests allowed local residents to charge traders high taxes for use of traditional grazing grounds for their animals.

"Policy planners in Kathmandu never considered what this would mean for us mountain people, they never thought about our needs," former Humla lawmaker Chhakka Bahadur Lama told AFP.

Unable to make ends meet, longtime herders like Tondhup Lama quit the trade, selling his yaks, sheep and horses to take up farming.

- End of an era -

Today, the few traders left say they have no other employment options and although they still travel to the China border, the Tibetan nomads have vanished and the trade has changed.

On sale at the border are cheap Chinese clothing, agricultural equipment and liquor.

Most agree that modernity must come to the neglected region, but lament the impending disappearance of the caravans.

"Our way of life is simply too primitive to survive in the modern age," ex-lawmaker Lama said.

"It's not just a question of a traditional economy ending, it's a culture melting away, it's the end of an era and a sad day in many ways."