Prime Minister Vladimir Putin Saturday dived to the bottom of the world's deepest lake aboard a mini-submarine, in a highly mediatized 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 (5,512 feet).

Russian news agencies said Putin had dived to a depth of around 1,400 metres (4,600 feet) -- 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.

Judo-mad Putin, 56, prides himself on keeping a peak physical condition and has raised eyebrows with a series of adventures over the last years.

Just the day earlier, he clipped a radio transmitter onto a beluga whale named Dasha in Russia's Far East.

Famous official pictures taken during his 2000-2008 presidency showed him fishing with a muscular naked torso that would impress any fitness fanatic while last year he fired a tranquilising dart at a tiger in the Far East.

But imagemakers have clearly been at pains to promote a softer side and the last months have seen him in unexpected situations ranging from singing in a classroom to denouncing the hunting of baby seals.

Back in his offices in Moscow, Putin has taken a front line role in fighting the economic crisis which has ended several years of dynamic growth in Russia and threatens impact its economy for years to come.

Putin has in the past also sailed on military submarines and even co-piloted a fighter jet. But RIA Novosti commented: "The dive on Mir-1 is one of the prime minister's most exotic experiments."