China is planning to extend its Tibet railway up to the Nepal border within the next five years, including a line that may pass through tunnels under Mount Everest, Chinese state media reported on Thursday.

A railway expert at the Chinese Academy of Engineering Wang Mengshu, who is China's most renowned expert on tunnel engineering, told the official China Daily that a line that is being built up to the Nepal border would likely "go through" Everest - a project that will, if given the green light, face enormous technical obstacles.

While China has given the go-ahead to extend the Tibet-Qinghai rail up to the Nepal border, the exact route and cost of construction are as yet undecided, according to officials.

"The line will probably have to go through Qomolangma (or Mount Everest) so that workers may have to dig some very long tunnels," Wang was quoted as saying.

As a result of the difficult terrain on the Tibetan plateau - the roof of the world - the trains would likely not be able to exceed 120 km/h, he suggested.

The China Daily said China and Nepal had discussed the extension of the network up to the Nepal border, which is set to be completed within the next five years. The line will extend from Shigatse (or Xigaze), which is connected to Lhasa, upto the border county of Jilong - a length of 540 km.

The line through Everest is not a certainty - Chinese planners have in the past proposed ambitious projects that have been stymied by cost considerations as well as strategic obstacles.

For instance, Wang told India Today in an earlier interview that a line had been proposed by planners linking China's southwestern border province of Yunnan to India as part of a sprawling pan-Asian network.

The India link appears unfeasible considering the boundary dispute and the slow-moving process of taking forward a long-discussed Bangladesh-China-India-Myanmar corridor. However, Beijing has made headway by taking forward rail links linking Yunnan to Laos and Thailand, with plans underway to extend the line up to Singapore.