From 2009, it will be possible to travel by train from Delhi to Srinagar, the capital of Jammu and Kashmir — a journey of 900km (560 miles). The 350km stretch, which is being built to complete the link, is hailed as “the most challenging railway project on earth”.

Not only are engineers blasting their way through the Pir Panjal mountain range, the first rampart of the Himalayas, they are also constructing the world’s highest bridge spanning the Chenab river in Kashmir.

At a height of 383m (1,257ft), the steel arch will be taller than the Empire State Building and stand 40m above the current record holder, the Millau Viaduct in the South of France.

Further testing Indian engineers is that the railway cuts through an uninhabited, inaccessible landscape without electricity, roads or water supply. The area is snowbound for most of the year and temperatures drop well below freezing.

“The technical aspect has never been attempted before,” said Vinoo N. Mathur, general manager of Northern Railway, the branch of India’s rail network responsible for the project. “We’re building a railway though a mountain range.” Making the environment all the more hostile is the railway’s journey into a warzone. An engineer at a building site and his brother have already been kidnapped and murdered by militants opposed to Indian rule in the Muslim region.

The threat from militants is a major constraint, according to officials. More than 1,200 labourers have to be moved between sites under security cover and are guarded by as strong a security force.

The railway is intended to integrate the restive region with the rest of India, Mr Mathur said. The project is also attempting to revive the once-thriving tourist industry that has been all but destroyed since the separatist insurgency against India erupted in 1989.

The 120km of tunnelling required for the passage through peaks as high as 4,000m is being made by vertically piercing a mountainside and then horizontally boring though granite, quartz and slate rock. The longest tunnel will be more than 11km.

The line falls into one of the Earth’s most seismically active zones, including the area hit by the earthquake last October. The tunnels withstood the disaster.

The railway will halve the time of the hairpin-road journey to the town of Jammu to six hours. “Most of the problems in Kashmir are related to its geographic and political isolation,” said Rekha Choudhary, Professor of Political Science at Jammu University.

“People cannot move easily to the rest of India and that has created a psyche of not being associated with it.”

Some Kashmiri academics question the gains the railway will bring. Nisar Ali, Professor of Economics at Kashmir University, said: “This region has been turned into a market for Indian goods and suffers from a dependency syndrome that has undone the state’s development since independence.” Professor Ali said that Kashmir was lacking basic infrastructure and had no electricity for up to 15 hours a day. “How will a railway get us out of this economic crisis?”

TRACK RECORDS

HIGHEST: Runs from Beijing to Lhasa reaching 5,072m

LOWEST: At 240m below sea level, the Seikan Submarine Tunnel, Japan

STRAIGHTEST: The 297-mile stretch across Nullarbor Plain, Australia

LONGEST: The 6,346-mile route from Moscow to Pyongyang, North Korea