Twice a year, a normally deserted border checkpoint high on the Tibetan plateau throngs with activity as traders from Nepal flock to do business with their giant northern neighbour China.

A biannual trade fair in Tibet offers a rare opportunity for those living in the remote former Buddhist kingdom of Upper Mustang in Nepal to cross the usually closed border into China, which is cultivating closer ties with the Himalayan nation.

"This trade is very important for us because we live in such an isolated area," said trucker Pasang Gurung, who was driving to China for the fair.

"Access to Chinese customers and products makes our lives much easier... I wish the border were open all the time."

The border is usually closed for security reasons as Upper Mustang has history as a base for the Tibetan resistance.

But authorities in Nepal are increasingly looked to strengthen economic ties with China and reduce its dependence on its other giant neighbour India.

But it will have a long way to go in order to accomplish that. Bilateral trade with India between July 2014 and June 2015 amounted to nearly $4.5 billion, dwarfing China's $882 million.

An energy agreement between Kathmandu and Beijing in March ended India's monopoly over fuel supplies to Nepal, although it remains the biggest supplier by far.

That deal was prompted by a months-long blockade at the border with India to protest the terms of a new national constitution that led New Delhi to halt supplies, leading to crippling shortages.

Kathmandu accused New Delhi of imposing an "unofficial blockade" in support of the protesters, an ethnic community that shares close family links with Indians across the border -- a claim India denied.

Sujeev Shakya, chairman of the Nepal Economic Forum think tank, says that even before the blockade India had a reputation in Nepal for being slow to deliver.

A number of Indian hydropower projects have stalled due to disagreements over the terms of the deal, while China has pressed ahead.

One 60-megawatt power plant is under construction and a 750-megawatt joint venture worth $1.6 billion is due for completion by December 2019.

"The perception here is that the Chinese tend to deliver while India keeps talking," Shakya told AFP.

"Over the years, China has gained more credibility in Nepal because of the pace at which they have put up infrastructure projects."

- Thriving trade -

In Upper Mustang's medieval walled capital of Lo Manthang, construction of a Chinese-funded 70-kilowatt solar power station last year has allowed residents to access electricity even during the months-long dry season, when hydropower supplies fall short.

Locals have welcomed the investment and are clamouring for deeper economic ties.

"If the border opens up, Lo Manthang can be a centre for trade, religious activities, tourism," said shopkeeper Kunga Dorje Gurung.

Around 1,000 visitors a day use the Korala checkpoint during the fair, trading in everything from carpets and clothing to tea and biscuits.

The journey has been made easier by a new road to the border that opened this year, and which locals hope will put pressure on Beijing to open the checkpoint more often.

"The road has made transportation of goods much easier," said Nepali businessman Tshering Phuntsok Gurung, travelling to the border with friends.

"Earlier, everything had to be carried on horses and the costs involved in hiring and feeding animals meant that the prices of the goods would also go up."

The thriving cross-border trade in Upper Mustang is particularly remarkable because the region was once the base for a CIA-funded guerrilla campaign to oust Chinese forces from Tibet after a failed uprising in 1959.

Thutop Dadhul, a Tibetan refugee, was just 17 when he and his family of nomadic herders fled Chinese troops and crossed over into Upper Mustang.

He threw himself into the Tibetan resistance movement, making daring trips across the border to gather intelligence.

"We had to win back Tibet... I am proud of the fact that I tried to do something for my country," the 75-year-old told AFP in the resort town of Pokhara, where tourist shopfronts display signs in Mandarin.

Outgunned on every front, the revolutionaries continued their fight even after the US government withdrew support in 1968 and only surrendered when the Dalai Lama asked them to lay down arms.

"I know the Chinese are being very generous to Nepal now, but that will change," he said.

"Eventually they will seek more control... and things will get worse for refugees like us."