China's multibillion railway to Tibet has not damaged the fragile ecosystem that it cuts through according to data gathered during the train's first year of operation, a top Tibetan environmental official said.

The US$4.2 billion project was built in four years on delicate permafrost, marshy ground easily damaged by human encroachment. Engineers installed sunshades and high-tech cooling columns plunged into embankments to help ensure the ground stays frozen.

China said last year it had earmarked US$190 million for environmental protection along the railway.

"The environmental bureau has been monitoring water, soil and air and the results show that there's no difference between the railway launch and now," said Zhang Tianhua, deputy director general of the environmental protection bureau of Tibet.

"I can tell you that definitively because I have statistics to back it up," he said but did not distribute the data.

Zhang said that since the train went into operation last July, no wastewater or garbage had been discarded or discharged along the new 710-mile stretch of rail linking Golmud in neighboring Qinghai province and Lhasa.

"I work specifically on environmental protection and I took the train June 1 and I didn't see any environmental pollution," he said.

He said the Chinese government was planning to set up an observation station to monitor the permafrost but gave no specifics.

"If the frozen earth melts, then the railway is gone," he said.