China has begun building the world's highest-altitude railway, connecting the far western province of Qinghai with Tibet. The railway will make it faster and cheaper to move people and goods into the region, but the project is fraught with controversy.

In the middle of the vast desert of China's northwestern Qinghai province, several dozen workers from around the country are laying railroad tracks, which will eventually lead to Tibet. They perform their backbreaking labor under the blazing sun for $2.50 a day. And for the glory of taking part in what may be one of the most ambitious engineering attempts in history: to build the world's highest altitude railway, winding over 1,100 kilometers of forbidding, snowcapped mountains from Golmud city in Qinghai to Tibet's capital, Lhasa.

Construction has only just begun, but Xia Jiaxiang, vice mayor of Golmud city, says the $3.3 billion Qinghai-Tibet railway will lure 50,000 workers to the area. Mr. Xia says most of the track will be laid on ground 4,000 meters above sea level, climbing to a peak of 5,000 meters, at the Tanggula Mountains on Tibet's border.

The railway project is so fraught with danger that teams of doctors with oxygen tanks have been dispatched to construction sites, to treat those with altitude sickness. Propaganda signs posted on the sides of some mountain refueling stops read "We can eat bitterness" and "We can endure hardship."

Fu Weixing, one of the doctors at a site 3,000 meters above the sea, says that anywhere above this level, productivity is very low. He says workers must be in top physical condition, and even then they tire easily and can only labor six hours a day. Construction will cease altogether during the frigid winter months.

But the challenges don't stop there. Half of the railway will be built on frozen earth, which risks melting in the summer.

Zhao Xinyu, chief engineer for the railway, says his team has the technology to prevent permafrost from melting. And asked about the railway's effect on endangered wildlife such as the Tibetan antelope, Mr. Zhao says corridors will be built below the tracks, for animals to cross without danger. He says the government will take care to protect the region's ecosystem.

But the railroad brings other concerns. Many Tibetans say the railway will consolidate Chinese control over their homeland, which has been occupied by Chinese troops since 1950, shortly after the Communists gained power.

A Tibetan native to Qinghai, who calls herself Tsering, says that the railway will bring a flood of Han Chinese to the area and dilute the already fragile Tibetan culture. She says she expects much more tension to develop between Chinese and Tibetans.

Vice Governor Baima of Qinghai province denies that China is building the railway for political control over the region. He asks, how much future can a poor region have if it relies solely on trucks for transportation? Mr. Baima says Tibet and Qinghai cannot develop without the railway, which is expected to be completed in 2007.

One ethnic Tibetan worker, a 34-year-old father of two, seems to agree with the government, saying that the railway will help tourism and transport. He himself has never been to Tibet. But asked if he wants to go there, he is stumped. Even if I wanted to go, he says, I can't afford the trip.