International organisations are appealing for funds to help prevent what one official warned could be the largest flood the world has ever seen.

Experts are afraid that Lake Sarez, in the Pamyar mountains of south-eastern Tajikistan, is in danger of spilling over.

The World Bank, the United Nations and Focus, a relief organisation linked to the Aga Khan, have just sent the first team of international experts to see if a large natural dam containing the lake will break, sending a torrent of water through Central Asia.

The World Bank is urgently trying to raise $4m to spend on an early warning system for local residents.

But officials are expected to tell a press conference in Geneva on Friday that much more is needed.

Catastrophe

The Tajiks have long been warning of the potential catastrophe if the lake ever breaks its banks.

Lake Sarez was formed by an earthquake earlier this century, and is held in by a 60m-high natural dam of rocks and boulders.

The fear has always been that the dam could break, unleashing a huge torrent of water that would sweep through large swathes of Central Asia.

International experts say from what they saw the dam is secure, but warned of the dire consequences if it is not.

"It's going to be the largest flood ever seen on planet earth by human beings for sure. The capacity of the lake is 17 cubic km. That's almost half the size of Lake Geneva and it's a 3,300m elevation so you imagine the energy," said Alessandro Palmieri of the World Bank.

Potential for destruction

If the dam did burst, the experts say the wave of water it would release could reach as far as the Aral Sea, 1,000km away, destroying villages and fields in its wake.

But they say much more likely at the moment is a landslide into Lake Sarez sending some of the water spilling over the dam down into the valley beyond.

Between 5,000 and 10,000 people live there and the UN and the World Bank say an emergency warning system is urgently needed to give them time to escape.