The 16-carriage train from the southwestern city of Chongqing derailed near Co Nag Lake, some 400 km northeast of the Tibetan capital, Lhasa, the Beijing News said, adding that only the dining carriage came off the tracks.

China opened the 1,140-km railway linking Golmud in Qinghai province to Lhasa on July 1, saying it would help modernise the isolated Himalayan region.

"Six trains were delayed along the line, affecting more than 4,000 passengers," Hong Kong's Beijing-backed Ta Kung Pao newspaper said.

Trains were running normally five hours later and no one was injured, it said, adding that an equipment failure involved switches and signals.

China, which has ruled Tibet since its Communist troops invaded the region in 1950, extols the railway as an engineering feat that will bring economic prosperity to the underdeveloped area.

But critics argue the line could endanger the region's fragile environment and Tibetans' unique cultural identity.

More than 960 km of the railway was built at 4,000 metres (13,120 feet) above sea level and 550 km in areas of frozen earth, which researchers fear could melt as winter temperatures rise in coming decades and affect operations.

Three passenger lines are carrying tourists in pressurised cabins to Tibet from Beijing and the cities of Chongqing, Chengdu, Xining, Lanzhou. Oxygen is on tap if needed.