Two Russian submersibles plumbed the depths of Lake Baikal in eastern Siberia on Tuesday, diving a record 1,680 metres (5,512 feet) in one of the world's largest lakes.

'It is a world record for deep-water submersion in fresh water,' an organizer told news agencies Itar-Tass on the barge fielding expedition that was to last another five hours.

The exploration mission is headed by pro-Kremlin lawmaker Artur Chilingarov, who led a mission with the same two mini-submarines to plant a Russian flag on the sea bed below the North Pole last August.

The Soviet-designed Mir-1 and Mir-2 submersibles are to scour Baikal's waters through mid-September for research on global warming and the local ecology and archeology.

Expedition captain, scientists Anatoly Sagalevich projected that the dive could discover new wildlife as well as new hydrocarbon reserves in what is the world's deepest lake.

Baikal is home to over 2,500 species, and environmental groups fear pollution is threatening the 25 million-year-old body of water.

The lake, which contains more than 20 per cent of the world's freshwater reserves, was declared a UNESCO World Heritage site in 1996.