Russia election: Vladimir Putin seeks third term
Russians are voting in presidential elections, with Vladimir Putin hoping to return to the post after four years as PM.
Mr Putin was head of state from 2000 to 2008, but barred by the constitution from standing for a third consecutive term. He faces four challengers.
Poll officials say turnout is higher than for the last election in 2008.
But opponents have reported widespread violations, with many people voting more than once.
The League of Voters volunteer observer group said it had recorded 3,000 violations in total.
Independent election watchdog Golos said it was hearing reports of so-called carousel voting, with busloads of voters being driven around to different polling stations, in Moscow and the Siberian cities of Novosibirsk and Barnaul.
Opposition blogger and anti-corruption campaigner Alexey Navalny told the BBC: "Grandiose scale of falsifications, especially in Moscow... mass use of carousel voting."
The election is being held against a backdrop of popular discontent, sparked by allegations of widespread fraud during December's parliamentary elections in favour of Mr Putin's United Russia party. Mr Navalny called for mass demonstrations on 5 March.
"A huge number of people will not recognise Putin as president and will continue to protest against him in different ways, including through street protests. Those will not stop. They will only increase," he said.
But Mr Putin's spokesman Dmitry Peskov seemed confident of victory.
"I think the elections will be legitimate, fair, and Putin will win in the first round, unless the court rules otherwise,"he told cable channel Dozhd TV.
Election officials said the turnout by 15:00 Moscow time (11:00 GMT) was nearly 48%, compared with 43% at the same stage in 2008.
Correspondents say there is real debate as to whether Mr Putin remains the best person to lead Russia, or whether the time has come for change.
Polls are open from 8am to 8pm in each time zone, with the first opening in the Far East of the country at 20:00 GMT on Saturday, and the last in the western Kaliningrad region closing at 17:00 GMT on Sunday.
Mr Putin voted in Moscow with his wife, Ludmila. Speaking afterwards to the Russian newspaper Izvestia, he said: "I'm expecting a good turnout, because presidential elections are an important event. I am confident that people will act responsibly".
Mr Putin's main challenger is considered to be Communist Gennady Zyuganov, who is running for a fourth time.
The other candidates are ultra-nationalist Vladimir Zhirinovsky, tycoon Mikhail Prokhorov, who is standing as an independent, and former upper house speaker Sergey Mironov, from the centre-left A Just Russia party.
If Mr Putin fails to achieve more than 50% of the vote he will face his nearest rival in a run-off.
However, the liberal opposition behind some of the recent protests is not represented.
The so-called white-ribbon movement has attracted more than 50,000 people in recent demonstrations in Moscow and other major cities, after widespread allegations of vote-rigging during elections for the State Duma. Similar numbers attended pro-Putin and pro-Communist rallies.
Mr Putin has responded by announcing a programme to install webcams in each of the country's 90,000 polling stations, but critics have questioned their effectiveness.
"Cameras cannot capture all the details of the voting process, in particular during counting," said a report by the Organisation for Security and Co-operation in Europe (OSCE), quoted by the Associated Press.
A joint mission by the OSCE and the Parliamentary Assembly of the Council of Europe comprising 250 observers is monitoring the elections.
Meanwhile tens of thousands of Russians have volunteered as election observers and been trained to recognise and report violations.