Voters in Argentina are going to the polls to select a successor to President Cristina Fernandez de Kirchner. She and her late husband had dominated the political landscape in the country for 12 years.
Sunday's election pits Buenos Aires provincial governor Daniel Scioli - Fernandez' chosen successor - against top rival Mauricio Macri, mayor of the same city.
Another major contender is Sergio Massa, a former ally of Fernandez and her late husband and ex-President Nestor Kirchner.
Massa launched a rival party, the Renewal Front, two years ago. He has been polling at around 20 percent - in comparison with some 40 percent for the favorite, Scioli, and around 30 percent for Macri.
As Argentine electoral law stipulates that a candidate must claim more than 45 percent of the vote, or at least 40 percent with a lead of 10 points over the runner-up, to win in the first round, it seems possible that the country could be headed for its first-ever run-off election.
If it does prove necessary, the second round would take place on November 22.
The poll marks the end of an era for Argentina, which was ruled by Kirchner and then Fernandez for 12 years. The pair pursued a populist "peronist" strategy based on trade protectionism and generous spending on social welfare programs.
Rival Macri has pledged to boost the country's economy, which is stagnant, with the International Monetary Fund predicting a 0.7 percent contraction next year. The inflation rate is also high, at about 30 percent.
Argentina is also still embroiled in a legal battle against two American hedge funds that reject the country's plans to restructure $100 billion (90.8 billion euros) in debt it defaulted on in 2001. The hedge funds successfully sued for full payment in a US federal court, leading to a new default last year when Fernandez refused to pay.
Some 32 million people are required to vote in the elections, and will also be electing representatives in Congress and the regional bloc Mercosur.
The first results are expected around 9 p.m. local time (midnight UTC).
tj/rc (AP, AFP)