The ruling party of Vladimir Putin on Monday won Russia's parliamentary elections but with a sharply reduced majority, in a blow for the strongman ahead of his planned return to the Kremlin in 2012.

The results mean his United Russia party has lost the constitutional majority of two-thirds in the State Duma required to pass any changes to the constitution, amid signs Putin's once invincible popularity is on the wane.

The vote on Sunday was shadowed by accusations of dirty tricks by the authorities and observers led by the OSCE said the elections were slanted in favour of United Russia and saw violations including ballot stuffing.

"The election administration lacked independence, most media were partial and state authorities interfered unduly at different levels," they said.

United Russia should obtain 238 seats in the 450-seat State Duma, an absolute majority but down sharply from the 315 seats it won in the last polls in 2007, election commission chief Vladimir Churov told reporters.

The party only managed to win 49.54 per cent of the vote, he said, a striking contrast from the 2007 polls staged when Putin's popularity was at its peak and his party won over 64 per cent.

"Based on these results, we will be able to ensure the stable development of our country," Putin said in a terse speech standing alongside President Dmitry Medvedev at his party's campaign headquarters.

Its biggest opposition will be the Communist Party with 92 seats, followed by the A Just Russia party with 64 seats and the ultra-nationalist Liberal Democratic Party with 56 mandates. The results are based on a 96 per cent vote count.

"United Russia only won a majority in the State Duma because of the particularities of Russian electoral law" the Vedomosti daily wrote, acidly describing United Russia as 'the party of the minority'.

The relatively poor showing came after Putin announced in September he planned to reclaim his old Kremlin job in March presidential polls, despite signs Russians may be growing disillusioned with his 11-year rule.

Putin, who has dominated Russia since 2000, is serving a four-year stint as prime minister after handing over the Kremlin in 2008 to his protege Medvedev.

Medvedev is set to step aside and become prime minister, in a job swap that the two men hope will determine Russia's political future and stability for years to come.

"The authorities are losing trust - it's a new situation for them," said Sergei Lukashevsky, head of the Andrei Sakharov Museum and Public Centre.

"The regime's ideology is exhausting itself."

Veteran liberal politician Grigory Yavlinsky's Yabloko party trailed in fifth place with 3.3 per cent of the vote, insufficient to qualify for seats.

In a sign the result could prompt a shake-up within the elite, Moscow Echo radio cited senior United Russia sources as saying that party chairman Boris Gryzlov would resign his post as Duma speaker.

The four years since the last parliamentary election have been marked by an outburst of criticism of the authorities on the Internet as web penetration of Russia started to finally catch up with the rest of Europe.

Putin was recently subjected to unprecedented booing when he made an appearance at a martial arts fight and opinion polls have shown an erosion in his once impregnable popularity.

"Who could have thought three days ago that, even with a distorted result, (United Russia) would poll less than 50 per cent," wrote top anti-corruption blogger and anti-Kremlin activist Alexei Navalny.

"I congratulate you all, we've done something great."

A string of news websites that do not toe the Kremlin line were down for election day on Sunday, including Moscow Echo, the Kommersant newspaper and The New Times magazine in an apparent mass cyber attack.

Meanwhile the website of the indepedent monitor group Golos, which exposed a string of violations in the campaign, was also paralysed after a week of harrassment by the authorities against its leaders.

The Communists, who won 19.6 per cent of the vote, complained the elections were hit by 'mass fraud' that turned them into a 'war zone'. The central election commission said that turnout was just over 60 per cent.

United Russia's popularity ratings varied widely across Russia - from over 90 per cent in regions in the majority Muslim Northern Caucasus to barely over 33 per cent on the Pacific region around the city of Vladivostok.