Poland is preparing for a snap election in which Jaroslaw Kaczynski, a leading presidential candidate, is bidding to replace his twin brother, whose death in April forced the early vote.
However, Kaczynski, who has campaigned to replace Lech Kaczynski, the late president, was trailing the ruling liberals' candidate in polls released ahead of Sunday's vote.
The election date was moved up after Lech was killed in a plane crash along with his wife and 95 others near the western Russian town of Smolensk on April 10.
Jaroslaw, a former prime minister and leader of the Law and Justice party, is scrambling to maintain a conservative presidency and keep the brakes on the policies of the governing, pro-EU Civic Platform party.
But Bronislaw Komorowski, the Civic Platform candidate and acting president, looks set to top the ballot on Sunday in a field of ten, with Kaczynski in second place, according to opinion polls.
"The Polish boat is sailing in the right direction," Komorowski said before a campaign blackout came into force at midnight on Friday.
Polling stations will be open from 04:00GMT to 18:00 GMT on Sunday.
Both Komorowski and Kaczynski held final rallies late on Friday in Gdansk, the Baltic port which was the cradle of the solidarity movement that drove Poland's communist regime from power peacefully in 1989.
Despite shared solidarity roots, there is no love lost between Civic Platform and Law and Justice, locked in a power struggle since 2005.
Opinion surveys show Komorowski may fall short of the 50 per cent of the vote needed for an outright win in order to avoid a July 4 run-off vote.
However, he would beat Kaczynski hands down in a second round, surveys show.
Victory would be a boon for Civic Platform, unlocking a political logjam more than a year before the autumn 2011 parliamentary elections.