Reporting from Moscow, Al Jazeera's Aleksandra Stojanovich-Godfroid said on Sunday the polls are viewed as a "major test" for the ruling United Russia party and President Vladimir Putin, who have both seen their ratings drop a year before parliamentary polls.

Tatyana Stanovaya, head of the R.Politik analysis firm, said the results of the polls will help the Kremlin determine whether United Russia needs to be reformed and if parliamentary elections should be pushed forward.

Led by Navalny, the opposition hopes to challenge Kremlin domination over Russia's political life by promoting tactical voting, urging Russians to back the strongest candidate on the ballot to defeat the ruling party.

Navalny's team urged Russians to vote for candidates from any party other than United Russia - Navalny had been in Siberia to promote the so-called "smart voting" when he fell ill.

Any other candidate - "a Communist, a Liberal Democratic Party member, a Just Russia party member" - would be "better than United Russia," Navalny's team said in a statement on Friday, referring to Russia's four major political parties.

With Navalny still recovering and absent from Russia's political scene, the "smart voting" campaign he had launched may be undermined, Stanovaya said.

One of the highest-profile campaigns has taken place in Novosibirsk, where the head of Navalny's office in Russia's third-largest city, Sergei Boiko, brought together the opposition to counter United Russia and the Communist Party.