The outspoken incumbent President Mr Zeman, who has pro-Russian and anti-immigrant views, leads opinion polls in the first round of voting against a crowded field of challengers.
The fierce critic has a 42.5 per cent chance of winning the first round, according to the most recent public poll by TNS Kantar & Median.
But the controversial populist could face a tougher threat from a single opponent in a run-off in two weeks if he does not win outright in the first round.
Final polls showed the most serious challenger was non-partisan academic Jiri Drahos.
Mr Zeman says he is an EU-federalist and that he favours a referendum on leaving the EU, although he would vote to stay in the bloc.
His more liberal rival Jiří Drahoš is staunchly pro-European and has called for Prague to “play a more active role in the EU”.
Meanwhile, Mr Zeman’s hardline approach to immigration from Muslim-majority countries has won him favour from large segments of the Czech public.
The Czech presidency is largely ceremonial but has an important role in picking who should form a government.
Mr Zeman’s victory is profoundly important to the recently installed prime minister, Andrej Babis, who heads up a minority government heavily dependent on the current president’s support for its survival.
The billionaire businessman said he would vote for Mr Zeman, 73, for his honesty, political experience and defence of national interests.
Mr Babis’s anti-establishment ANO party won more than twice as many seats as any other group in an October vote but still fell far short of a majority.
He told a news conference: “I see him as a strong personality which is polarising society, but mainly as someone who does not steal, who has results, who keeps his word… and unlike other politicians, he does not live from politics, he lives for politics.
“He is a man who fights for our national interests, he is not afraid to clearly state his opinion on Brussels, (migration) quotas, he fights for the interests of our entrepreneurs.”
Mr Babis stressed that any government he leads would hold a foreign policy course based on the country’s EU and NATO membership.
Mr Zeman’s first five-year term ends on March 7, giving time for more talks before then on forming a government, regardless of who wins the election.
If the talks stretch out beyond then, Mr Babis may have a harder time with some of Mr Zeman’s opponents.
The main reason why most other parties refuse to work with Mr Babis is that he faces investigation over whether he illegally tapped European subsidies as a businessman 10 years ago.
He denies any wrongdoing.
Mr Babis is facing a confidence vote for his minority government next week with almost no chance of winning.
Mr Zeman has promised to give Babis a second chance to form a government if the first attempt fails.
The Czech lower house on Wednesday postponed the confidence vote until January 16 or later as lawmakers tussled over the fraud allegations and whether to lift his parliamentary immunity to allow prosecution.