Prime Minister Vladimir Putin yesterday dived to the bottom of the world's deepest lake aboard a mini-submarine, in a highly mediatised stunt unusual even by the standards of the Russian hardman.

Putin, wearing special thermal blue overalls, was able to examine the unique flora and fauna of Lake Baikal in Siberia during his four-hour journey underwater aboard the Mir-1 submarine.

"I've never experienced anything like it in my life," the prime minister, who served eight years as Russian president, told state television aboard the support ship after resurfacing.

"It's a special feeling. What I saw impressed me because with my own eyes I could see how Baikal is, in all its grandeur, in all its greatness," he added.

The lake's mythological beauty has always held a special place in the heart of Russians and is its fresh waters are home to a variety of endemic species, most notably the Baikal seal.

"The dive is going perfectly, there is a perfect view with the lights," Putin told Russian journalists from the depths of the lake on a crackling radio link-up during the dive.

However he expressed some surprise about how murky the water was in the lake, which contains around a fifth of the world's freshwater reserves. "The water, of course, is clean from an ecological point of view but in fact it's a plankton soup, or so I called it," he said.

The Mir-1 is the same mini-submarine that in 2008 set a world record for the deepest dive in a lake by diving to 1,680 metres.

Russian news agencies said Putin had dived to a depth of around 1,400 metres - the deepest point in the lake's southern part - and safely returned to the surface after four hours underwater.

Excited Russian journalists even asked Putin on his return if he now intended to visit the International Space Station (ISS) for his next exploit but he played down this idea.

"On earth there is a lot of work to do," the RIA Novosti news agency quoted Putin as saying.