MOSCOW: Russians voted on Sunday in presidential polls expected to return strongman Vladimir Putin to the Kremlin for a record third term, despite a wave of protests against his 12 years of domination.

Voters from Vladivostok on the Pacific to the Kaliningrad exclave on the Baltic will cast their ballots in a marathon election stretched over 21 hours in which victory for 59-year-old ex-KGB spy Putin appears inevitable.

But the newly-emboldened opposition has promised protests after the elections and the polls were proceeding amid heavy security with Moscow police drafting in 6,300 extra officers.

"We are going to respond to provocations with the full force allowed by law," warned Moscow police chief Vladimir Kolokoltsev in a briefing with Russian media.

The looming protests mean Putin's expected landslide victory against four rivals may be tainted by political uncertainty unknown during the current prime minister's first two terms as president between 2000 and 2008.

"I'm choosing a new Russia. Everything is just beginning," the first of Putin's rivals to cast their ballot, the metals magnate turned politician Mikhail Prokhorov, said as he voted in the Siberian city of Krasnoyarsk.

But despite the recent demonstrations, state-run pollsters have forecast a first-round win for Putin with 60 percent of the vote, leaving his Communist rival Gennady Zyuganov trailing in second place with 15 percent.

Prokhorov and the flamboyant populist Vladimir Zhirinovsky are expected to battle for third place while the former upper house speaker Sergei Mironov is tipped to finish last. But there are no candidates representing the fledgling protest movement.

"I know Putin for practical actions, not words," pensioner Zinaida Bykova told AFP in Vladivostok after voting for the man who has dominated Russian politics for more than a decade.

"Every vote is important when you live in a democratic country," another voter, student Anna Antipenko, told AFP.

Turnout in the Far-Eastern region of Kamchatka to the north was 46 percent by mid-afternoon local time, over 10 percent more than in the parliamentary elections in December, local officials told Russian agencies.

Reports of a high early-morning turnout in the region could indicate a potentially similar pattern nationwide, said the head of Russia's central election commission, Vladimir Churov.

Street protests that erupted in response to alleged fraud during December's parliamentary ballot have swelled into a broader opposition movement whose use of online networks has echoed the Arab Spring revolts.

Putin, who has served a four year stint as premier under the presidency of Dmitry Medvedev, would be taking on a six year mandate at a time when Russia is undergoing dramatic social change 20 years after the USSR collapse.

"We live under Putin's hand already many years, and nothing is changing in the country," said 45-year-old Yulia, who has cast her vote for Prokhorov at a station in southwestern Moscow.

"He is a new face in Russian politics, it's a conscious choice to vote for him and I hope that he wins. But it's unlikely," she said.

The authorities have installed web cameras in 90,000 polling stations for the first time in an attempt to demonstrate transparency and combat allegations of cheating.

The cameras were switched on overnight, including in polling stations that are normally used as social clubs meaning that some broadcast Saturday night dancing parties live -- much to the amusement of Russian bloggers.

Voting in Moscow began with unprecedented participation by volunteer election monitors armed with cameras and phones, who vow to stop any dirty tricks such as falsifying results or stuffing ballots.