Ukrainians are voting in a runoff election pitting incumbent President Poroshenko against comedian Volodymyr Zelenskiy. Zelenskiy has been leading in opinion polls.
Ukrainians were at the polls on Sunday in elections that could see a comedian with no prior political experience become president.
Recent opinion polls show Volodymyr Zelenskiy, who has already achieved national fame by playing the part of a president in a popular TV series, well ahead of incumbent President Petro Poroshenko. The polling agency Rating gave Zelenskiy 73% to Poroshenko's 27%.
"The victory today will be Ukraine's," Zelenskiy said at a polling station in Kiev. "We have united the country ... everything will be all right." The comic was later fined, according to his campaign manager, for violating election rules by showing his anonymous ballot to reporters.
After casting his ballot, Poroshenko said "it's important to be guided by reason, not laughs," adding that "it could be funny first, but pain may come later."
Zelenskiy's pledge to step up the fight against corruption has gone down well with the electorate in a country where just 9% of the population trusts the national government, according to a Gallup poll published in March.
"There is a hope that a simple man will better understand us and dismantle the system that we have in our country," a Zelenskiy voter said on election day, according to French news agency AFP.
Other voters noted, however, that with no allies in parliament, Zelenskiy's tenure may not last long.
'Not a comedy you can turn off'
Poroshenko had launched a last-minute plea on Facebook, telling Ukrainians "a five-year presidential term is not a comedy that you can easily switch off if it is no longer funny."
Zelenskiy's unorthodox style and background in entertainment have drawn comparisons to Italy's Beppe Grillo or to US President Donald Trump. However, despite his pledge to tackle corruption, some questions have been raised about his ties to oligarch Igor Kolomoysky, whose TV channel broadcasts Zelenskiy's shows.
The new president will face several challenges, including a Russian-backed insurgency in the east of the country. Ukraine also remains one of Europe's poorest countries almost 30 years after it won independence from the Soviet Union.
Both candidates have vowed to keep the country on a pro-Western course if elected.
Thirty million Ukrainians are eligible to vote. Exit polls are expected around 8 p.m. local time, with official results following several hours later.
mm, tj, es/jm (Reuters, dpa)