No joke, this comedian could become Ukraine's next president

Comedian Volodymyr Zelensky topped the first round of Ukraine's presidential election Sunday, exit polls showed, setting him up for a run-off with the incumbent after voters expressed frustration over corruption and a stalling economy.

When he announced his long-shot candidacy at the start of the year, Zelensky's political experience had been limited to playing the president in a television show.

But he tapped into fatigue with the political class to overtake President Petro Poroshenko and knock ex-prime minister Yulia Tymoshenko out of the race.

"This is just a first step towards a great victory," the 41-year-old in high spirits told supporters at his campaign headquarters minutes after the exit polls were released.

"We're not relaxing."

If the actor wins the second round in April, as opinion polls suggest, he will take the reins of one of the poorest countries in Europe - a nation of 45 million people fighting Russian-backed separatists in its industrial east.

At a voting station earlier in the day he had promised a Ukraine "without corruption, without bribes".

The entertainer was projected to garner around 30 per cent of the vote, handily beating Poroshenko on about 18 per cent, according to combined figures from three pollsters.

Towards midnight local time just over one per cent of the vote had been counted and fuller official results were not expected until at least morning.

Poroshenko said the projected results were a "harsh lesson" for him personally and for authorities as a whole.

He said he felt "no euphoria" in reaching the second round and said the results should provide an impetus to "work on our mistakes".

Tymoshenko, who was herself a favourite to win when she launched her campaign at the start of the year, was knocked out with around 14 per cent, the figures showed.

But Tymoshenko, who rose to international prominence as a charismatic face of the 2004 Orange Revolution, claimed the exit polls were "dishonest".

Taking her third tilt at the presidency, the 58-year-old insisted she had come in second place and told supporters to wait for final results.

Zelensky has yet to spell out what he would do in power and one of his campaign slogans was: "No promises. No apologies."

Despite concerns about his vague platform, supporters insist only a brand new face can clean up Ukraine's murky politics.

Some accuse Zelensky of acting as a front for the interests of oligarch Igor Kolomoysky, who owns the channel that broadcasts the entertainer's shows, but he denies any political links.

The actor has eschewed rallies and interviews in favour of playing gigs with his comedy troupe up to the final days of campaigning.

His political comedy Servant of the People returned for its third series last week.

Poroshenko - a chocolate magnate who was one of the country's richest men when he took office - came to power in 2014 after a revolution forced his pro-Russian predecessor out of office.

The popular uprising was followed by Russia's annexation of Crimea and the separatist conflict in eastern Ukraine.

The 53-year-old leader said he would shut down the fighting, tackle corruption and align the country with the West.

But five years on, the conflict has claimed some 13,000 lives and counting, while many feel Poroshenko has failed to live up to the promise of the revolution.

The campaign saw allegations of corruption and fraud from all sides.

A record 39 candidates were on the ballot paper - which was more than 80cm long - but none apart from the front runners reached double figures, according to the exit polls.

The head of the central election commission said the vote took place without "systemic violations" though the interior ministry earlier said it had received more than 1,700 reports of voter irregularities.

Turnout was 63 per cent, up around 4 per cent on the previous presidential election, according to provisional figures from the election commission.

Zelensky and Poroshenko will face off for the presidency on April 21.