Poles vote in a presidential election, seen as a struggle for the country’s future and its strained relations with the European Union.
The second round beats incumbent Andrzej Duda, an ally of the Conservative government, against the socially liberal Warsaw mayor Rafal Trzaskowski.
A Duda win would lead to controversial changes in the judiciary and continued opposition to abortion and gay rights.
Trzaskowski supports a more progressive agenda and an active role in the EU.
Mr Duda topped the first round of voting with a convincing lead but did not reach the 50% needed to win directly.
But Mr Trzaskowski expects to win the support of most of those who voted for other candidates, and a close result is predicted.
Surveys were opened at 07:00 local time (05:00 GMT) and closed at 21
BBC’s Adam Easton, who reports from a polling station in Warsaw, says there is a steady stream of people arriving and putting on face masks to vote, but no signs of the long queues seen two weeks ago in the first round, which saw the highest turnout in 25 years.
President Duda is an ally of the ruling Nationalist Law and Justice Party (PiS) and if he loses, the opposition can push through major changes in Polish politics.
The president has the power to veto legislation, so Mr. Duda’s re-election would be of use to PiS, as he used to be a member.
He came under fire during the election, including for a speech in which he said that LGBT rights were an “ideology” more destructive than communism.
Speaking on the final day of the campaign on Friday, Duda said that Duda would continue to strengthen the Polish state, “built on our inviolable tradition that is sacred to all of us and where we have grown up for generations.”
Trzaskowski has promised to heal with the European Union.
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Liberal politicians rose quickly in the elections after joining the race in May. Former member of Donald Tusk’s Liberal Civic Platform Government, he won the capital’s run for mayor in 2018, promising “Warsaw for all.”
He said that Polish voters would never get another chance to change Poland’s direction.
“Everything is in your hands,” he said on Friday. “This [electoral victory] is really at hand. I want to tell you “now or never” because this law and fair road roll will try to run over everything and the next election can be very difficult. “