Engineers have modified parts of the route along the Qinghai-Tibet plateau because it passed too close to the habitats of certain species, such as the black-necked crane.

Global warming was also taken into account to stabilize the track, with systems installed to ensure the ground remains frozen along the 550 kilometers (340 miles) where the line is anchored in permafrost.

"We will protect the environment like the pupils of our eyes," the chairman of the Tibetan Autonomous Region, Champa Phuntsok, told foreign journalists in the regional capital of Lhasa.

The railway official in charge of the line, Zhu Zhensheng, said "protection of the vegetation in a cold, high-altitude area and protection of wildlife, lakes, wet lands and areas of permafrost" were top priorities.

Such assurances, however, mean little for critics who point to China's notoriously bad environmental record across the rest of the country and see the train line as opening the flood gates to similarly bad practices in Tibet.

Nearly three decades of economic "development" has seen China become home to many of the world's most polluted cities, with the environment consistently sacrificed in the drive to modernize.

The government conceded last month that the nation's environmental woes were steadily growing and costing the economy around 200 billion dollars each year.

"The trend of increasing environmental degradation has not been effectively controlled," the State Environmental Protection Administration said in a report.

The report listed excessive logging, degraded pasture land, shrinking wetlands and overuse of fertilizers and pesticides as major problems.

"Excessively fast development will put a lot more pressure on the environment and this kind of development is not sustainable," Zhu Guangyao, vice minister of the administration, said as he released the report.

Tibet, located mostly at an altitude of more than 4,000 meters (13,200 feet) above sea level and cut off from the rest of China by high mountains, has largely avoided the devastation because of its inaccessibility.

Saturday's opening of the train line, which runs 1,142 kilometers from the mountain outpost of Golmud in China's far northwestern Qinghai province to the Tibetan capital Lhasa, has changed all that.

Already thousands of extra tourists have visited Tibet in the first few days of the train line's operation, while many majority Han Chinese are expected to migrate to the region in what critics say is a deliberate "colonization" ploy by Beijing.

"An additional surge of Chinese migrants will only result in greater deforestation, degradation of the grasslands and soil erosion," Free Tibet Campaign spokesman Matt Whitticase said.

Whitticase pointed our that the impact would be felt not just by China, but across the region, with Tibet being the source of several of the world's great rivers.

"The plateau is an area where the waters of 10 of the world's largest rivers divide, including the Indus, Mekong, Yangtse, Bhramaputra and Salween," he said.

Chinese economist Zhang Xiaode of the National Institute of Administration also voiced his fears for the fragile environment.

"It is an area which is thirsty for development. The tourist boom and the increase in the number of means of transport will exert an influence on the environment," he said, calling for a law to protect the Tibetan ecosystem.

"I am an economist, not an environmental expert, but it is very possible that what (environmental damage) you already see in other areas of China could also happen here."

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