Brazilians were voting on Sunday in the most unpredictable presidential election in decades and the first since the end of an economic boom underpinning the leftist Workers' Party's 12-year rule.
As President Dilma Rousseff seeks a second term, voters are weighing whether the socioeconomic gains of the last decade are enough to reject the candidacies of a popular environmentalist and a pro-business social democrat, who both promise to jump-start the economy after four years of lackluster growth.
Polls show Rousseff as the front runner in a race that is likely to go to a runoff on Oct. 26.
"It really is too close to call," said Rafael Cortez, a political analyst with Tendencias, a consultancy in Sao Paulo. "Volatility and frustration favor opposition candidates, but you don't really have a crisis to topple the government, either."
Lines formed early Sunday as citizens prepared to cast ballots when voting started at 8 a.m. local time.
Rousseff's main rivals are Marina Silva, a hero of the global conservation movement with the Brazilian Socialist Party, and Aecio Neves, a senator and former state governor from the centrist party that laid the groundwork for Brazil's economic boom last decade.
Even after mass protests a year ago, driven by the economic malaise and anger over corruption and poor public services, Rousseff remains the favorite, helped by a barrage of negative campaigning that eroded an early lead by Silva.
More than 140 million people are registered to vote in Brazil, where everyone between the ages of 18 and 70 is required to cast a ballot. Voting is computerized, meaning results are expected just a few hours after polls close in western states on Sunday afternoon.