The sons of Sir Edmund Hillary and Tenzing Norgay told British newspaper The Independent that their fathers would no longer recognise the world's highest mountain, saying the base camp is now 40 metres (132 feet) lower than it was 53 years ago.

"Climate change is happening. This is a fact," Hillary's son Peter said.

"Base camp used to sit at 5,320 metres. This year it was at 5,280 metres because the ice is melting from the top and side. Base camp is sinking each year," said Peter Hillary, who himself has twice reached Everest's summit.

"For Sherpas living on Mount Everest this is something they can see every day but they can't do anything about it on their own," he added.

The glacier where Hillary and Tenzing made their base camp before ascending the 8,848-metre (29,198-foot) summit on May 29, 1953 has retreated three miles (five kilometres) in the past 20 years, The Independent said.

Scientists, it said, predict that all glaciers in the Himalayas, which range from half a mile to more than three miles long, could end up as small patches of ice within 50 years if global warming is not checked.

"The glaciers have receded a great deal since my father's time," said Jamling Tenzing, who climbed Everest with Peter Hillary in 2002.

"There are many things he wouldn't recognise today. The glacier on which base camp sits has melted to such a degree that it is now at a lower altitude. I think the whole face of the mountains is changing," he said.

Peter Hillary warned of devastating effects if glaciers continue to melt, form huge lakes and then burst their banks.

"I've seen the result of glacial lakes bursting their banks and it's catastrophic," he was quoted as saying.

"It's like an atomic bomb has gone off. Everywhere is rubble. The floods of the past are nothing compared with the size of what we are threatened with," he added.

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