Russia faces a massive crisis including economic collapse and social tensions if Vladimir Putin rather than Dmitry Medvedev stands in presidential polls, two Kremlin advisers warned on Wednesday.

In the most vocal call yet for Medvedev to seek a second mandate in 2012 elections, the advisers from the Institute of Contemporary Development (INSOR) painted a bleak picture of a future Russia with Putin again in the Kremlin.

Medvedev and Putin -- who left the presidency in 2008 after two mandates to become prime minister -- have not yet made clear who will stand in the March polls other than insisting they will not run against each other.

"The sheer fact of the current president deciding not to continue his mandate will cause a major crisis in the country," INSOR chief Igor Yurgens and board member Yevgeny Gontmakher wrote in an article for daily Vedomosti.

Their institute was set up by Medvedev when he took over the presidency to advise on economic policy. It is seen as one of the most radical supporters of his trademark modernisation policy within the Russian establishment.

If Medvedev decides not to run, they forecast a sharp fall in the Russian markets and a rapid worsening of two of the country's biggest existing problems -- capital flight and immigration abroad.

Social problems and right-wing extremism could also rise, they wrote.

Openly attacking Putin as a conservative strongman, Yurgens and Gontmakher said the Russian prime minister was "now leading an open political campaign for continuing the course of 'stability'".

Stability, they wrote, has become in Russia a synonym "not even of stagnation but of a clear decay in all areas of Russian life."

"For such a political, economic and social catastrophe, Putin would not even need to return directly to the president's office. It would be enough for a third figure to appear from the prime minister's circle," the pair added.

They said that Medvedev needed to cross "his personal rubicon" and call on society to work together "in the difficult task of pulling the country out of the quagmire that we have fallen into."

Putin announced on Tuesday that ruling party United Russia would hold its annual congress on September 23-24, an event where the announcement of the presidential candidate could finally be made.

Whichever of the men stands, he is almost certain to win, given the lack of opposition and the unstinting support of state media for the political establishment.