DEEP in the Qilian Mountains in northwest China, early spring arrives with heavy snow and freezing temperatures. In this desolate spot in Qinghai Province, at an altitude of 3,700 meters above sea level, migrant worker Li Bingui is seldom separated from his jackhammer, which makes his whole body shudder as he breaks apart bedrock.

Li, along with more than 1,800 other workers, are at the mercy of a brutal environment as they construct the world's highest high-speed passenger railway. It's also controversial because of extremely high cost and what is expected to be low ridership because of high ticket costs.

The workers are carving out a 9,490-meter-long tunnel through the rugged mountain range, one of the most difficult segments of the line to link Lanzhou, capital of Gansu Province, with Urumqi, capital of the Xinjiang Uygur Autonomous Region.

The 1,776-kilometer second line of Lanxin Railway runs across Gansu and Qinghai provinces to Xinjiang, traversing the wind-ravaged Gobi Desert.

Started in late 2009 and scheduled to be completed in 2015, the line is designed for trains traveling at up to 300 kilometers per hour, much faster than the current 120 kilometers per hour on the existing line - cutting travel time between Lanzhou and Urumqi to about six hours.

Ren Shaoqiang, chief engineer with the China Railway 20th Group Co Ltd that in charge of the construction, says that compared with the Qinghai-Tibet Railway and the existing line between Lanzhou and Urumqi, construction of this fast-rail line is more challenging.

"Take the tunnel project, for example. There's no precedent to draw from," says Ren, who also played a significant role in building the Qinghai-Tibet Railway, the highest rail link in the world. "We have to make innovations, just as we did on the Fenghuoshan Tunnel of the Qinghai-Tibet Railway."

In the past year or so, engineers have worked with researchers from several Chinese universities on natural disaster forecasting, water discharge, and measuring of wall rock transfiguration, among other things.

Other worries are more immediately pressing, such as the lack of oxygen in the air because of the high altitude, which poses health threat to workers.

Zhang Hong, a director at the site, says natural oxygen content in the tunnel is only around 65 percent of that in low-lying areas.

And, from October to June, the mountain is frequently covered by ice and snow.

Construction worker Wu Xuelin says working on the site is far more stressful than working on similar projects in coastal areas like in Shandong Province or Shanghai.

"I could not adapt well to the altitude at the beginning, suffering headaches, nausea, and I had difficulties sleeping," Wu says.

The company has improved safety measures, providing workers with oxygen tanks and setting up rooms at cave exits where workers can inhale oxygen. It has also built oxygen-generating stations to provide more oxygen in the tunnel.

Live video surveillance and alarm systems have been set up.

"We only need to switch on a computer and log in to our accounts to know what's happening in the tunnel, even if we are thousands of kilometers away," Ren says. "We can also remotely control operations."

"Under such conditions, nobody can stand a high workload for a long time," says Guo Yuhong, secretary of the Communist Party of China and Union Committee for the Qilian Mountains Tunnel.

Guo, 44, has been stationed at the construction site since last year, and his hair has turned gray during that period of time.

Costly, controversial

According to Ren, building the line through difficult terrain like in the Qilian Mountains requires twice as much investment compared with similar high-speed line construction on low-level flat areas.

Workers' wages has been doubled, he says.

For regular high-speed rail lines with a designed speed of 350 kilometers an hour, construction costs can reach 100 million yuan (US$15.5 million) per kilometer, much higher than lines for trains traveling at 200 kilometers per hour.

As the first long-distance high-speed rail line in western China, the second line of Lanxin Railway has a planned investment of more than 140 billion yuan, but the actual figure is not yet known.

The project, designed as a passenger route, will allow the existing Lanxin Railway to be used exclusively for freight.

Analysts are divided over whether the benefits outweigh the costs of building high-speed lines in the ecologically fragile western regions.

Some say higher construction costs will only push up ticket prices and, like other high-speed lines in coastal areas, might not meet favor with many passengers. Others call it an effective means to develop the economy in the generally under-developed regions.

A senior researcher with the China Academy of Railway Sciences says, on condition of anonymity, that it will be difficult to make money from building such a line.

"It's more of a political thing," he says. "It's more about national defense and ethnic unity."

The new railway is expected to facilitate transport of energy resources from the vast desolate northwest to other regions of the country.

Take Xinjiang for example. Rich in oil, coal and natural gas reserves, the region is expected to supply more of its resources to other areas in the coming five years.

Wang Tieshan, a PhD in economics at the Xi'an Jiao Tong University, says high-speed railways are vital for closer links between widely separated cities in the western region.

So far, several provinces and regions in the west, including Shaanxi Province in the northwest and Guizhou in the southwest, have laid out ambitious plans for high-speed rail construction over the next five years.

Currently, high-speed rail has linked Xi'an, capital of Shaanxi Province, with Zhengzhou, capital of central China's Henan Province. More such links between Xi'an and other western cities like Chengdu and Yinchuan are either under construction or in the planning.

At the political sessions held in early March, high-speed rail remained one of the hottest topics among national legislators and political advisers, particularly as the high-growth industry was shrouded in uncertainties following the sacking of former railway minister Liu Zhijun on suspicion of graft.

Sheng Guangzu, the new railway minister, says Liu's case was only an individual one and that China would continue to develop the industry in the coming years in accordance with the country's mid-and-long-term railway network plan.

Under China's economic master plan unveiled in March for the next five years, China aims to have more than 16,000 kilometers of high-speed railway by 2015. Currently, more than 8,000 kilometers of high-speed rail line are in operation, already the most in the world.

As to concerns about the massive debts caused by high construction costs and low occupancy rate due to expensive tickets, Sheng says the debt ratio of around 56 percent is "normal" and "controllable."

Sheng also has pledged strict and high-quality standards on the construction of high-speed rails to ensure safety.

However, legislators and political advisers have called for a brake on the expansion of the high-speed rail network to avoid over-investment driven by what they call an irrational pursuit of speed.

Political adviser Feng Pei'en suggests that new railway construction plans be made public to solicit feedback and that decisions be made based on objective analysis of passenger flows by air, rail and road.

Zhuang Wei, another political adviser, argues that China should focus on building railways with speeds of around 250 kilometers per hour because those higher than 300 kilometers an hour are not only much more expensive but also tend to produce more pollution.