Across dizzying 5,500 metre-high mountain ranges that stretch across the ‘roof of the world’ are hundreds of kilometres of newly-laid expressways, bridges and tunnels that China is building in Tibet.

In Yadong county, which lies just across the Nathu La Pass from Sikkim in the Chumbi valley, plans are underway to extend China’s most ambitious railway project in history.

In 2006, China’s engineers unveiled the terrain-defying Qinghai-Tibet railway, cutting through the Tibetan plateau and opening up Lhasa to the Chinese hinterland for the first time.

China has already upgraded the roads from Lhasa to Yadong. A 500km journey to the India border took Mail Today only seven hours

Officials in Yadong have told Mail Today that the line from Lhasa is now in the process of being extended across a 500km distance, all the way to the border county of Yadong.

Tests on the line, which will connect Lhasa right up to Nathu La Pass and Sikkim, may begin in less than two years’ time.

Last year, the Lhasa line was extended by 250km to Xigaze, which is not far from the Nepal border. The line to Yadong will be the second extension of the Lhasa line.

The Xigaze rail, which was put into operation last year, halves the travel time from Lhasa to just two hours.

Local officials in Yadong say a line running to the India border could transform the currently paltry $15million border trade, which relies on a small border market that is open from Monday to Thursday in Yadong.

But the plans will also have strategic implications, by extending Tibet’s railway network right up to the border.

Later this year, a third line will be built to Nyingchi, which borders Arunachal Pradesh.

China has already upgraded the roads from Lhasa to Yadong. A 500km journey to the India border took Mail Today only seven hours.