Pro-Russian Czech President Milos Zeman faced-off against more liberal pro-European rivals as voting got underway Friday in a two-round presidential election that saw the incumbent targeted by a bare-breasted anti-Kremlin protester.

Opinion surveys show the divisive 73-year-old ex-communist, who is also staunchly anti-Muslim and pro-Chinese, leading the pack of nine candidates ahead of Jiri Drahos, 68-year-old pro-European former head of the Czech Academy of Sciences.

Although Zeman is in pole position, the outspoken head of state is unlikely to win an outright majority and is set to face a run-off vote on January 26-27.

The topless protester, from the Ukraine's Femen group, called Zeman "Putin's slut," before being overpowered by bodyguards and taken into custody by police.

Security personnel also had to help a visibly rattled Zeman, who walks with a cane, to leave the room.

Asked whether the incident could sway the vote, independent political analyst Jiri Pehe told AFP it was "hard to say" but that reactions on social media were sympathethic to Zeman, and "not just among his supporters".

Prague voter Martin Sauta said he voted for Zeman as he has "the most consistent views",

"The other candidates are completely shapeless, I can't see a reason to vote for any one of them," he told AFP.

But Prague wine bar owner Eva Simova, 53, told AFP that he was voting for Drahos: "He seems like an honest guy and what's more, I'm sick and tired of Zeman."

A recent poll commissioned by Czech Television showed Drahos winning a second round vote with 48.5 percent of the vote against 44 percent for Zeman.

- Unite or divide? -

Zeman's rhetoric echoes other populist-minded eastern EU leaders -- especially in Hungary and Poland -- at odds with Brussels over mandatory refugee quotas and various rules they see as attempts to limit national sovereignty.

He is also stridently anti-Muslim, having once called the 2015 migrant crisis "an organised invasion" of Europe and insisted Muslims were "impossible to integrate".

Paradoxically, the country of 10.6 million people has received only 12 migrants under the EU quota system.

Drahos could not be more different. A mild-mannered liberal centrist whom critics have dubbed "wishy-washy", he has called for Prague to "play a more active role in the EU" and has backed the adoption of the euro currency.

After voting in Prague Friday, Drahos told reporters that the future president "should work in the interest of the pro-Western orientation of the Czech Republic" in a clear dig at Zeman.

"The president should work to unite society. It's clear that not everyone can agree, but the current president doesn't unite people, he divides them," Drahos added.

- Liberal democracy? -

Analyst Pehe said the vote showed "how society is polarised".

"It is a clash between... the post-communist part of society represented by Zeman and the other part, say, modern, pro-Western, which simply doesn't want this president any more," he told AFP.

Zeman has won the backing of embattled billionaire Prime Minister Andrej Babis, who said on Thursday he thought the incumbent "fights for our national interests" but called on Zeman to "unite, not divide" Czechs.

Babis, whose populist ANO movement scored a landslide win in general elections last October with its anti-corruption and anti-euro campaign, will need to be on good terms with the next president.

Potential coalition partners have shunned the Slovak-born tycoon who is facing police charges over EU funding fraud, making it impossible for him to form a majority government after Zeman tapped him for prime minister.

Babis appears set to lose a parliamentary confidence vote scheduled for January 16.

Pehe said a victory for Zeman might "pave the way for a deeper alliance with Andrej Babis, which could lead to a change in some basic parameters of liberal democracy in the country."

But the situation could change dramatically if Drahos wins.

"Drahos has made it very clear that a prosecuted man should not be prime minister," Pehe said.

Zeman's other rivals include ex-gambler and songwriter Michal Horacek, and former right-wing premier Mirek Topolanek.

The CTK news agency pegged turnout at 40 percent after day one of voting.

Polling stations reopen at 0700 GMT on Saturday before closing at 1300.

Soon after that initial results will indicate which two candidates are likely to contest the expected run-off vote.