Brazilians are voting in an election that could determine if the country returns a leftist to the helm of the world’s fourth-largest democracy or keeps the far-right incumbent in office for another four years.
Sunday's race pits incumbent President Jair Bolsonaro against his political rival, former president Luiz Inacio Lula da Silva.
There are nine other candidates, but their support pales to that of Bolsonaro and da Silva.
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Voting stations opened at 7 am local time (1100 GMT). All polls will close at 5 pm local time (2000 GMT), regardless of areas that are in later time zones.
Recent opinion polls have given da Silva a commanding lead - the last Datafolha survey published on Saturday found that 50 percent of respondents who intend to vote for a candidate said they would vote for da Silva, against 36 percent for Bolsonaro.
The polling institute interviewed 12,800 people, with a margin of error of plus or minus two percentage points.
Latin America leaning left
Bolsonaro’s administration has been marked by incendiary speech, his testing of democratic institutions, his widely criticised handling of the Covid-19 pandemic and the worst deforestation in the Amazon rainforest in 15 years.
But he has built a devoted base by defending traditional family values, rebuffing political correctness and presenting himself as protecting the nation from leftist policies that infringe on personal liberties and produce economic turmoil.
A slow economic recovery has yet to reach the poor, with 33 million Brazilians going hungry despite higher welfare payments.
Like several of its Latin American neighbours coping with high inflation and a vast number of people excluded from formal employment, Brazil is considering a shift to the political left.
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Gustavo Petro in Colombia, Gabriel Boric in Chile and Pedro Castillo in Peru are among the left-leaning leaders in the region who have recently assumed power.
There is a chance da Silva could win in the first round, without the need for a run-off on October 30.
For that to happen, he would need more than 50 percent of valid votes, which exclude spoiled and blank ballots. Brazil has more than 150 million eligible voters, and voting is mandatory, but abstention rates can reach as high as 20 percent.
An outright win would sharpen focus on the president’s reaction to the count given he has repeatedly questioned the reliability not just of opinion polls, but also of the electronic voting machines.