Ukraine launched a new massive wave of drone attacks Sunday as Russians cast ballots on the final day of a presidential vote set to extend President Vladimir Putin's rule for another six years.

Air defences in eight Russian regions including the capital Moscow shot down 35 unmanned aerial vehicles, one of which sparked a fire at an oil refinery overnight, authorities said.

In Russia's border city of Belgorod, Ukrainian shelling killed a 16-year-old girl and wounded her father, the region's governor said.

"Kamikaze drones" also set a polling station ablaze in the Russian-controlled part of Ukraine's Zaporizhzhia region on Sunday without causing casualties, according to Moscow-installed authorities.

The 71-year-old Putin, a former KGB agent, has been in power since the last day of 1999 and is set to extend his grip over the country until at least 2030.

If he completes another Kremlin term, he will have stayed in power longer than any Russian leader since Catherine the Great in the 18th century.

He is running without any real opponents.

The Kremlin has cast the election as an opportunity for Russians to show they are behind the war on Ukraine, where voting is also being staged in Russian-held areas.

In a pre-election address on Thursday, Putin said Russia was going through a "difficult period".

"We need to continue to be united and self-confident," he said, describing the election as a way for Russians to demonstrate their "patriotic feelings".

The voting will wrap up in Kaliningrad, Russia's westernmost time zone, at 1800 GMT and an exit poll is expected to be announced shortly after that.

A concert on Red Square is being staged on Monday to mark 10 years since Russia's annexation of Ukraine's Crimea peninsula -- an event that is also expected to serve as a victory celebration for Putin.