A letter from Pyotr Sumin, governor of the Chelyabinsk region, to the Russian prime minister, Mikhail Kasyanov, warned of a potential catastrophe if the main dam bursts, as more than 400M m3 of radioactive waste is stored in reservoirs around the mountains.

Sumin warned that water levels were becoming dangerously high and appealed for action.

The Chelyabinsk region has been dubbed one of the most radioactively contaminated zones in the world. It is also at the centre of Russian plans to import the world’s nuclear waste for safekeeping.