Russian media are reporting cases of vandalism at polling stations, possibly carried out by people who oppose the presidential election that is almost certain to keep Vladimir Putin in power.

Three-day voting began on Friday across Russia. Putin and three other candidates are on the ballot.

But the incumbent is all but assured to win his fifth term, because candidates who criticize Russia's invasion of Ukraine were not allowed to run.

Russian media says a woman set fire to a voting booth at a polling station in Moscow. Security camera footage shows flames coming from the booth after she approached it.

A video taken at another polling station in the capital shows a woman pouring what appears to be a green dye into a transparent box containing ballots.

Similar incidents have been reported in polling stations in the second largest Russian city of St. Petersburg, a city in Siberia and elsewhere.

Russia's Central Election Commission warns that people who obstruct voting face up to five years in prison.