China's railway to Tibet, opened this month to great fanfare, is developing cracks in its concrete structures while its permafrost foundation is sinking and cracking.
"The frozen ground that forms the foundation of the railway is sinking and cracking in some sections, making the railway unstable in some places," the Beijing News quoted railway ministry spokesman Wang Yongping as saying.
"The concrete is cracking on some of the railway structures and bridges, forming a hidden danger to the railway line quality."
President Hu Jintao opened the railway to the Tibetan capital of Lhasa July 1, calling it a magnificent engineering feat and a miracle for the world.
The 4.2-billion dollar railway which runs 1,142-kilometers (713 miles) from the desert outpost of Golmud in Qinghai province to Lhasa, the regional capital of Tibet, is the highest in the world.
It climbs a peak of 5,072 meters (16,737 feet) above sea level along the Tibetan plateau, with the railway using supposedly state-of-the-art cooling techniques to ensure the permafrost foundation remains frozen.
Wang added that shifting sands in the region were also causing greater harm to the railway than expected, while engineers had still not figured out how to keep herds of yaks off the tracks, the report said.
"These form dangers to passengers on the train," he said.
Climatologists monitoring global warming last year said that rising temperatures could lead to the melting of the permafrost foundation of the railway, but said nothing about the frozen ground sinking or cracking.
"By 2050, safe operation of the Qinghai-Tibet railway will be affected if temperatures keep rising steadily as observed over the past decades," the China Daily quoted a climatologist as saying at a Beijing symposium last year.
Railway spokesman Wang did not say how engineers would address the problems.
The government sees the rail line as an important tool in modernizing and developing Tibet, which has been part of China since Chinese troops "liberated" the region in 1950.
However critics argue the line will allow the national majority Han Chinese to flood in to Tibet, leading to the devastation of the local Tibetan culture, as well as accelerate environmental degradation of the pristine region.
Previously Tibet could only be reached on slow, uncomfortable bus rides or on relatively expensive flights. On the new train, people can travel for 48 hours from Beijing to Lhasa for under 50 dollars.