Zuzana Caputova, a vocal government critic, was expected to take the lead in round one of the Slovak presidential election on Saturday.
The Slovak Statistics Office said 45-year-old Caputova had 39.14 percent of the vote, with ballots from 50 percent of polling stations counted.
Read more: Slovakia's presidential election focuses on corruption, democracy
Her strongest challenger, Maros Sefcovic, a 52-year-old career diplomat and European Commission vice president backed by the ruling Smer-Social Democracy party, came in a distant second with 18.77 percent. If no single candidate wins a majority on Saturday, a runoff will be held on March 30.
Opinion polls have given Caputova, a lawyer and environmental activist, a double-digit lead over Sefcovic in the race for the largely ceremonial post. Caputova would be Slovakia's first female president, if elected.
It's the first vote held since the murder of investigative journalist Jan Kuciak and his fiancee last February, which dealt a blow to the political establishment.
"I see a strong call for change in this election following the tragic events last spring and a very strong public reaction," Caputova told reporters as she cast her ballot in her hometown, Pezinok. "We stand on a crossroads between the loss and renewal of public trust, also in terms of Slovakia's foreign policy orientation."
Read more: Murder of Jan Kuciak: What did Slovakia's government know?
Caputova was among tens of thousands of protesters who took to the streets after the killings, which shocked the nation and raised fears about media freedom and political corruption.
Kuciak and his fiancee, Martina Kusnirova, were shot to death in February 2018 just before he was due to publish a story on alleged ties between Slovak politicians and the Italian Mafia.
The double murder threw the country into turmoil, and demonstrations after their deaths were the largest anti-government protests in Slovakia since communist times.
Read more: Slovakia at an economic crossroads
The central European country of 5.4 million people spent decades behind the Iron Curtain before joining the European Union, the eurozone and NATO.
Following the murders, then-Prime Minister Robert Fico was forced to resign. However, he is still the leader of the populist-left Smer-SD party and a close ally of current premier Peter Pellegrini.
Four people were charged with the killings. On Thursday, prosecutors said they had also charged multimillionaire businessman Marian Kocner with ordering the murder of Kuciak, who had been investigating his business activities at the time. It is thought that Kocner has ties to Smer-SD.
law/cmk (AFP, AP, Reuters)
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