What you need to know:
- Poroshenko said the projected results were a "harsh lesson" for him personally and for authorities as a whole.
- 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.
Comedian and political novice Volodymyr Zelensky topped the first round of Ukraine's presidential election on Sunday, exit polls showed, leading incumbent Petro Poroshenko into a run-off.
Zelensky's political experience had been limited to playing the president in a TV show but his long-shot bid won over voters frustrated with endemic corruption and a stalling economy.
"This is just a first step towards a great victory," the high-spirited 41-year-old told supporters at his campaign headquarters minutes after the exit polls were released. "We're not relaxing."
At a voting station earlier in the day he had promised a Ukraine "without corruption, without bribes".
The entertainer was projected to garner 30.4 percent of the vote, handily beating Poroshenko on 17.8 percent, according to combined figures from three pollsters.
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".
Ex-prime minister Yulia Tymoshenko, who was herself a favourite to win when she launched her campaign at the start of the year, was knocked out with 14.2 percent, 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.
If Zelensky wins the second round in April, as opinion polls suggest, the actor 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.
He 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.
Zelensky 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 this 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 graft 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.
Tymoshenko, who rose to international prominence as a face of the 2004 Orange Revolution, was taking her third tilt at the presidency.
The campaign saw allegations of corruption and fraud from all sides.
A record 39 candidates were on the ballot paper -- which was more than 80 cm long -- but none apart from the frontrunners reached double figures, according to the exit polls.
The interior ministry said an hour before the close of polls that it had received more than 1,700 reports of voter irregularities.
Turnout by mid-afternoon was at 45 percent, up five percent on the same time during the previous presidential election, according to the central election commission.
If the results of the exit polls are confirmed, Zelensky and Poroshenko will face off for the presidency on April 21.