In India, the Gangotri glacier is receding at an average rate of 23 metres per year, the study said.

"Himalayan glaciers are among the fastest retreating glaciers globally due to the effects of global warming," the WWF said in a statement.

"This will eventually result in water shortages for hundreds of millions of people who rely on glacier-dependent rivers in China, India and Nepal," it said.

"The rapid melting of Himalayan glaciers will first increase the volume of water in rivers causing, widespread flooding," said Jennifer Morgan, director of the WWF's global climate change programme.

"But in a few decades this situation will change and the water levels in rivers will decline, meaning massive economic and environmental problems for people in western China, Nepal and Northern India," she said.

WWF released the study before a two-day ministerial roundtable in London this week of the 20 greatest energy-consuming countries, to be followed by a G8 meeting focusing on climate change in Africa.

Himalayan glaciers feed into seven of Asia's greatest rivers, the Ganges, Indus, Brahmaputra, Salween, Mekong, Yangtze and Huange He.

The glaciers ensure a year-round supply of water to hundreds of millions of people in China and the Indian subcontinent.

The WWF called for work toward reducing carbon dioxide emissions -- blamed for global warming -- plus increasing the use of renewable energy and energy-saving measures.

The countries participating in the "Energy and Environment Ministerial Roundtable" include Canada, France, Germany, Italy, Japan, Russia, the UK and the United States plus non-G8 countries Australia, Brazil, India, China, Indonesia, Iran, Indonesia, Iran, Korea, Mexico, Nigeria, Poland, South Africa, and Spain.