Vladimir Putin sought a convincing victory in Russia's presidential election on Sunday to strengthen his hand in dealing with the biggest opposition protests since he rose to power 12 years ago.

Critics question the legitimacy of a vote they say is skewed to help the former KGB spy return to the Kremlin after four years as prime minister, and are threatening to step up protests that began after a disputed parliamentary poll in December.

Putin's victory was not in doubt as voters cast ballots from Russia's Pacific coast across many sparsely populated swathes of territory to the western borders with the European Union. But he was hoping for an outright victory in the first round which he could portray as a strong mandate for six more years in power.

Early signs were that turnout would be high. Officials said more than 12 percent of voters had cast ballots by 10 a.m Moscow time (0600 GMT) compared with 8.9 percent at the 2008 election that brought Putin's ally, Dmitry Medvedev, to the Kremlin.

Some voters expressed anger at being offered no real choice in a vote that pits Putin against four weaker candidates - communist Gennady Zyuganov, nationalist Vladimir Zhirinovsky, former parliamentary speaker Sergei Mironov and billionaire metals tycoon Mikhail Prokhorov.

Others said Putin, who has portrayed himself as a man of action, was the tough national leader Russia needed.

'I will of course vote for Putin. Who else is there?,' said Mikhail, a university student in Vladivostok, a port city of 600,000 on the Pacific coast.

'I voted for the Soviets,' said an aged man dressed in a shabby leather coat who declined to give his name. Asked if that meant Zyuganov, he said: 'For Putin. He is raising our pensions, while Zyuganov is only making pledges.'     

The last opinion polls before the election showed Putin, who was president from 2000 to 2008 before constitutional limits barred a third straight term, would win 59-66 percent of the vote, enough to avoid a second-round runoff.  

Putin, 59, has been lionised by state television and is running against politicians who, with the exception of Prokhorov, have made a habit of losing elections to the Kremlin. - Reuters