An emergency committee set up to cope with the disaster said several hundred other people had complained of feeling unwell.

The sodium cyanide was being transported in cylinders to Kyrgyzstan's main gold mine when a truck carrying it crashed spilling its cargo.

Many of the peaks in the Tien Shan or Clestial mountains remain unclimbed

The cyanide leaked into the river, which feeds the country's largest lake and main tourist attraction Issyk-Kul.

Issyk-Kul is one of the largest Alpine lakes in the world, more than a thousand metres up in the high Tien Shan mountains and to the Kyrgyz is a symbol of great national pride.

Sodium cyanide is used extensively in Central Asia as a separating agent in gold mines.

Official assurances

The BBC's Central Asia correspondent says stories have quickly spread of dead animals found near the shores of the lake and of strange smells emanating from the water.

However, local officials have reassured people that the lake is perfectly safe, even swimming in the water in front of a party of journalists.

Also the Canadian Kyrgyz company, Kumtor, which manages the mine where the chemical was being taken, has assured local residents that there is no cause for alarm. It has warned though not to drink the water.

Independent scientists say the shear size of Lake Issyk-Kul, which is more than 150 km long, means it is likely that most of the toxic chemical will have been quickly diluted without harm to the local habitat.

But the BBC correspondent says there is little doubt that the incident will have raised concerns about the safety of such dangerous cargoes on Kyrgyzstan's winding mountain roads.