The ambitious plan has been on the drawing boards for many years. It has advantages for both parties. Beijing would have direct access to the Arabian Sea; currently, 80 per cent of China’s oil travels through the Indian Ocean and the Strait of Malacca, an area plagued by piracy. More importantly, in case of war, China’s enemies could easily block its oil supplies. Pakistan would especially benefit from increased traffic in the Gwadar port, which was built with Chinese capital and assistance and opened in 2008.

Now the railway, which until recently appeared to be technically impossible because of the difficult terrain, at 5,000 metres above sea level, could be built thanks to the experience and knowledge China has accumulated during the construction of the Qinghai-Tibet railway.

However, Professor Wang Mengshu, a rail expert at Beijing Jiaotong University, said that the Kashgar-Gwadar project would be "more difficult than the one in Tibet" because Chinese surveyors and mappers will not have as good an understanding of the local terrain as they did in Tibet.

This would also create uncertainties about the cost, which Wang estimates would be around 200 million yuan (US$ 30 million) per kilometre, a bill too great even for Beijing.

In addition, India is not going to look favourably at closer Sino-Pakistani relations. New Delhi has always regarded Islamabad as its main adversary and Beijing as its main rival.

In fact, the proposed railway would have to pass through Pakistan-administered Kashmir, a territory claimed by India, and would thus undermine the latter’s its claim. Indeed, important Indian newspapers have described the project as a serious threat to India's security.

However, the idea still has many supporters in China and many see its completion as only a matter of time.

People's Liberation Army Navy Rear Admiral Yin Zhuo said China relied too heavily on sea transportation for its oil imports. Hence, "We must either build a much more powerful navy or find alternative transportation channels."