Ukraine has entered uncharted political waters after exit polls showed a comedian with no political experience and few detailed policies had easily won enough votes to become the next president of a country at war.
The apparent landslide victory of Volodymyr Zelenskiy, 41, is a bitter blow for incumbent Petro Poroshenko who tried to rally Ukrainians around the flag by casting himself as a bulwark against Russian aggression and a champion of Ukrainian identity.
Two national exit polls on Sunday showed Zelenskiy had won 73 per cent of the vote with Poroshenko winning just 25 per cent. Early voting data suggested the polls were accurate.
Zelenskiy, who plays a fictitious president in a popular TV series, is now poised to take over the leadership of a country on the front line of the West's stand-off with Russia following Moscow's annexation of Crimea and support for a pro-Russian insurgency in eastern Ukraine.
Declaring victory at his campaign headquarters to emotional supporters, Zelenskiy promised he would not let the Ukrainian people down.
"I'm not yet officially the president, but as a citizen of Ukraine, I can say to all countries in the post-Soviet Union look at us. Anything is possible!"
Zelenskiy, whose victory fits a pattern of anti-establishment figures unseating incumbents in Europe and further afield, has promised to end the war in the eastern Donbass region and to root out corruption amid widespread dismay over rising prices and sliding living standards.
But he has been coy about exactly how he plans to achieve all that and investors want reassurances that he will accelerate reforms needed to attract foreign investment and keep the country in an International Monetary Fund program.
The United States, the European Union and Russia will be closely watching Zelenskiy's foreign policy pronouncements to see if and how he might try to end the war against pro-Russian separatists that has killed about 13,000 people.
Zelenskiy said on Sunday he planned to continue European-backed talks with Russia on a so far largely unimplemented peace deal and would try to free Ukrainians imprisoned in Russia, which is holding 24 Ukrainian sailors among others.
Viktor Medvedchuk, the Kremlin's closest ally in Ukraine, last week outlined ways in which Ukraine and Russia could mend ties, though Zelenskiy has given no indication of being open to the prospect.
Russian foreign ministry spokeswoman Maria Zakharova said Ukraine now had a chance to "reset" and unite its people.
An emotional Poroshenko conceded defeat to his supporters, some of whom were crying. Although he said he accepted the loss, he said he would not be leaving politics and that Zelenskiy would face strong opposition.
Zelenskiy has pledged to keep Ukraine on a pro-Western course, but has sounded less emphatic than Poroshenko about possible plans for the country of 42 million people to one day join the European Union and NATO.
Poroshenko said on social media he thought Zelenskiy's win would spark celebrations in the Kremlin.
"They believe that with a new inexperienced Ukrainian President, Ukraine could be quickly returned to Russia's orbit of influence," he wrote.
Critics accuse Zelenskiy of having an unhealthily close working relationship with a powerful oligarch called Ihor Kolomoisky, whose TV channel broadcasts his comedy shows.
Zelenskiy has rejected those accusations.
