(CNN) -- Poland's presidential election produced no clear winner Sunday, official results showed, so the top two candidates will face each other in a runoff.
Interim President Bronislaw Komorowski had just over 41 percent of the vote with 94 percent of the vote counted, the National Electoral Commission said on its website.
That put him in first in a field of 10 candidates, but short of the the 50 percent needed for outright victory.
Jaroslaw Kaczynski came second, with slightly under 37 percent of the vote.
The special election is to replace Kaczynski's twin brother, Lech, who was killed in a plane crash in April.
Komorowski, the speaker of parliament, became acting president on Lech Kaczynski's death. The runoff election will likely take place July 4.
The vote was originally planned for the autumn but brought forward after Kaczynski's death.
Jaroslaw Kaczynski, once prime minister, is a divisive figure in Polish politics. His far-right Law and Justice party runs on a nationalist platform with the slogan, "Poland comes first."
"Poland has to be a strong country, otherwise it will not exist," he said recently. "I want to tell everyone here that as president I won't just be the head of state -- I will look after the strength of the Polish nation."
Komorowski is a moderate running for the center-right Civic Platform.
"We have been on this road for 21 years together and we have been right," Komorowski said on the campaign trail. "We have been moving toward democracy and navigating our way in a free economy."
The tragic death of the president and recent fatal floods in southern Poland -- which left at least 20 people dead and caused hundreds of millions of dollars in damage -- have meant a tame presidential campaign.
Political analyst Radoslaw Markowski described the race as "less aggressive" and said the candidates have avoided straightforward debate. Though the president in Poland is primarily a ceremonial figure, he has the power to veto laws, thus helping to shape politics.
President Lech Kaczynski, his wife and more than 90 others were killed in western Russia in April on their way to the 70th anniversary of the Russian massacre of Polish prisoners of war in the village of Katyn.
CNN's Fred Pleitgen contributed to this report