The trial runs at Lake Baikal lasted two hours with two submarines diving to a depth of around 420 metres (1,386 feet), the Russian media reports quoted the organisers as saying.

On Tuesday, the expedition will begin in earnest with the submarines attempting to descend 1,637 metres (5,402 feet) to the bottom of the lake which has a unique ecosystem and has never been explored.

The expedition is being organised by Artur Chilingarov, a pro-Kremlin member of parliament and an Arctic explorer who led the team of scientists that planted a flag at the bottom of the North Pole in August last year.

Previous missions have only descended hundreds of metres.

Scientists will collect samples at different depths and hope to document the effects of global warming on the lake, as well as drawing the attention of the Russian government to the need for greater environmental protection.

The mission at Lake Baikal -- a UN World Heritage site which contains around a fifth of the world's freshwater reserves -- will carry out dozens of dives by the Mir-1 and Mir-2 mini-submarines.