Putin, who rose to power in 1999, is poised to win a new six-year term that, if he completes it, would make him Russia’s longest-serving leader for more than 200 years.

The election comes more than two years since Putin triggered the deadliest European conflict since World War II by ordering the invasion of Ukraine in what he casts as a defensive “special military operation”.

War hangs over the three days of voting that ends on Sunday: Ukraine in recent days repeatedly attacked oil refineries in Russia with drones, shelled Russian regions and sought to pierce Russian borders with proxy forces – a move Putin said would not be left unpunished.

Putin, 71, has warned the West that any meddling in the vote would be considered an act of aggression.

While his re-election is not in doubt given a lack of any significant rival candidate, Putin wants to show that he has the overwhelming support of Russians.

The Kremlin has sought a high turnout and as polls opened for a third day in western Russia, officials said the turnout in the first two days had already reached 60 per cent nationwide.

An exit poll will be published shortly after voting ends at 1800 GMT.

Supporters of Alexei Navalny, who died in unexplained circumstances at an Arctic prison in February, called on Russians to come out at a “Noon against Putin” protest to show their dissent against a leader they cast as a corrupt autocrat.

“Alexei was fighting for very simple things: for freedom of speech, for fair elections, for democracy and our right to live without corruption and war,” Navalny’s widow, Yulia, said in a message to a rally in Budapest on Friday.

“Putin is not Russia; Russia is not Putin.”

There was no independent tally of how many of Russia’s 114 million voters turned out at noon to show opposition to Putin, amid extremely tight security involving tens of thousands of police and security officials.

Reuters journalists witnessed a slight increase in the flow of voters, especially younger people, at noon at some polling stations in Moscow and Yekaterinburg, with queues of several hundred people.

Some said they were protesting.

Hundreds of Russians stood in line at noon at polling stations at Russian diplomatic missions from Australia and Japan to Armenia, Kazakhstan and Georgia.

During the previous two days, there were scattered incidents of protest as some Russians set fire to voting booths and poured dye into ballot boxes, drawing a rebuke from Russian officials who said they were scumbags and traitors.

Opponents posted some pictures of ballots spoiled with slogans insulting Putin.

Angela Stent, senior non-resident Fellow at the Brookings Institution, said the election outcome was not in question but there were serious reasons to take note of the event.

“Vladimir Putin will win, probably by a landslide, and he will claim increased legitimacy as a successful war leader on March 18,” Ms Stent told the Russia Matters project at Harvard Kennedy School’s Belfer Center.

“The Russian presidential election matters to the United States and its allies for two reasons – what happens during the voting period and what follows after it is over.”

The West, which has supplied Ukraine with hundreds of billions of dollars of aid, weapons and top-level intelligence, says Putin is engaged in a brutal imperial-style war aimed at restoring some of the clout of the Soviet Union.

Russian and Ukrainian estimates indicate that hundreds of thousands of soldiers on both sides have been killed or seriously injured, although neither side gives proper casualty figures.

Swathes of Ukraine have been devastated.

Putin casts the war as part of a centuries-old battle with a declining and decadent West that he says humiliated Russia after the Berlin Wall fell in 1989 by encroaching on what Putin considers to be Russia’s sphere of influence such as Ukraine.

Russian officials say the West is engaged in a hybrid war against Russia that will include trying to meddle in its election and cast doubt on its results.