Election officials denied any significant fraud in polls that gave Putin well over 60 percent of the vote in initial results and exit polls while Putin's campaign chief trumpeted "the cleanest elections in the history of Russia."

But opposition leaders defiantly dismissed the result, pointing to evidence of violations in a vote monitored by tens of thousands of volunteers.

Communist leader Gennady Zyuganov, who is likely to poll second, complained the vote was "crooked, absolutely unfair and unworthy."

"I think the real level of support of Putin in Russia is no more than 41 percent," protest movement leader Alexei Navalny said in comments on his Russian Elections website after initial results.

"There's no such thing as a pro-Putin Russia and an opposition Russia. There's just one Russia where the people see a huge number of votes being stolen."

Such views countered televised assurances from Central Electoral Commission chief Vladimir Churov that the polling stations were "working perfectly."

A record number of more than 27,000 observers monitored the vote, according to coordinating website Control2012.ru, after protest leaders urged a close watch following December's fraud-tainted parliamentary vote.

The Control2012 website listed more than 5,000 violations after the announcement of initial poll results.

Tycoon Mikhail Prokhorov, who is projected to come third, wrote on Twitter that his supporters had "recorded more than 4,000 violations."

Gazeta.ru website posted a video from a polling station in Dagestan in the North Caucasus, showing several men feeding a stream of ballot papers into electronic ballot boxes.

Putin's campaign chief, Stanislav Govorukhin, later backed a probe.

In another online video, a vote observer in the Urals city of Yekaterinburg filmed police detaining around 10 minibus passengers who said they had voted several times.

In a scam dubbed a "carousel" in Russian, voters are bussed around polling stations to vote multiple times, using absentee ballots, with the help of corrupt officials.

"The 'carousel' voters were detained and handed to the police," Rostislav Zhuravlev, an observer from the Communist party, wrote on Facebook.

Navalny's Russian Elections site aired an interview with a woman who gave her name as Kristina, who said she took part in a similar scam.

Kristina said she voted twice and organisers paid voters 5,000 rubles ($171), Navalny wrote on Twitter.

A pro-Kremlin youth group said it bussed regional activists around Moscow to vote, raising suspicions of vote tweaking in the city with the largest anti-Putin protests.

Young people from provincial towns waited in hundreds of buses parked on Moscow's central Bolotnaya Square on Sunday, an AFP correspondent witnessed.

"I came here to vote for Vladimir Vladimirovich," said one young man from the Far Northern city of Belomorsk, more than 1,000 kilometres (600 miles) from Moscow.

Nashi pro-Kremlin youth group acknowledged 20,000 of its members were attending Moscow rallies and it had taken them to polling stations to vote.

Observers said absentee ballots were being used on such a massive scale that polling stations ran out of the forms.

"In Moscow and the Far East they ran out of absentee ballots despite the fact that extra copies were printed by the central election committee," said the head of the Golos monitoring group, Liliya Shibanova.

Senior Communist official Valery Rashkin alleged violations including bribes of 1,000 rubles ($30) paid to voters in far eastern Russia for backing Putin.

Writing on the party website, he called the polls "the dirtiest elections of the past eight years."