China's western glaciers are melting so fast that they may have largely disappeared by the end of the century, drying up parts of the rivers they currently feed, the official Xinhua agency reported on Monday.

The rivers of ice on the Qinghai-Tibet Plateau, which borders the Himalayas and has been nicknamed the "roof of the world", account for around four-fifths of China's glaciers, Xinhua said.

But over the last three decades, they have retreated at a rate of around 131 kilometres a year, largely because of global warming, the report said.

"If the glaciers continue to melt at the current speed, most of them will have disappeared and rivers in their lower reaches will have dried up by 2100," Yao Tandong, head of the Chinese Academy of Science's Qinghai-Tibet Plateau Research Institute, told Xinhua.

The region is the source of several of Asia's most important and iconic rivers, including the Yangtze, Indus and Mekong, so a fall in water levels could potentially affect hundreds of millions of people.

The melting is also having a more immediate effect upstream, where multiplying pools of water are building up, flooding residents along rivers -- and then bursting, endangering people living downstream, recent reports have said.

A National Climate Change Assessment released last year predicted a slower glacier retreat; by 2100 glaciers on the Qinghai-Tibet highlands could shrink by two thirds, it said.

But Greenpeace in a report on China's threatened glaciers cited one forecast that 80 percent of the glacial area in Tibet and surrounding parts could disappear by 2035.

Nationwide, glaciers have shrunk by seven percent, or 389 cubic kilometres, since the 1960s, research by Yao's team shows.

China on Monday unveiled a national plan to tackle climate change, which did not directly mention glaciers but warned that the country had already seen a fall in runoff across six key rivers over the last 40 years.