President Rakhmonov of Tajikistan has called for help from Russia and his Central Asian neighbours to stop a lake in the south-east of the country from overflowing, warning that it could have grave consequences for the whole region.

The Sarez lake is 3,000 metres up in the great Pamir mountains and scientists have been warning for years that the natural dam of mud and rocks which holds in the lake's waters is unstable and could burst, unleashing a tidal wave which could reach up to 1,000 kilometres away.

The lake itself was formed by an earthquake 80 years ago. Huge landslides brought mud and rock tumbling down the mountainsides, forming the natural dam which today holds the waters in.

Earthquake zone

The fear has always been that another earthquake or rock fall could burst the fragile structure, unleashing a huge torrent of water which some say could form a wave 70 metres high.

Experts warn that such is the volume of water it would sweep through villages and fields from Afghanistan to the south to Uzbekistan and Turkmenistan to the north and west.

Even if the dam held, the lake is surrounded by massive crags of rock, some the size of five-storey buildings. If one fell, scientists say, water would again be sent racing down the valleys.

The dangers have been known since Soviet times but since the collapse of the Soviet Union little has been done. Tajikistan has been racked by civil war and it is only recently that attention has again turned to trying to make Lake Sarez safe.

The Pamir mountains are an earthquake zone and Tajik officials now say last month's quake just across the border in Afghanistan has created new cracks in the rocks.