The initial vote tally showed Bolsonaro with 51.5% of votes compared with 48.5% for Lula with 20.8% of voting machines counted, although the Workers Party tends to be stronger in regions that are slower to report results.

Lula allies on Sunday said police had stopped buses carrying voters on highways even though the electoral authority had prohibited them from doing so. Brazilian media reported that such operations were concentrated in the northeast, where Lula has the strongest support.

"What happened today is criminal. There is no justification for the (police) to mount roadblocks on Election Day," Workers Party President Gleisi Hoffman told journalists.

However, the Superior Electoral Court (TSE), which runs Brazil's elections, said no one had been prevented from voting and declined to extend voting hours. The Federal Highway Police said they had complied with court orders.

The election serves as a referendum on two starkly different - and vehemently opposed - visions for Brazil's future.

Bolsonaro has vowed to consolidate a sharp rightward turn in Brazilian politics after a presidency that witnessed one of the world's deadliest outbreaks of COVID-19 in the pandemic and widespread deforestation in the Amazon basin.

Lula promises more social and environmental responsibility, recalling the rising prosperity of his 2003-2010 presidency, before corruption scandals tarnished his Workers Party.

Bolsonaro has without proof described the voting system as fraud-prone, raising concern he may not concede defeat, following the example of his ideological ally, former U.S. President Donald Trump.

That has added to tensions in Brazil's most polarizing election since its return to democracy in 1985 after a military dictatorship that Lula, a former union leader, rallied against and Bolsonaro, a former army captain, invokes with nostalgia.

With Bolsonaro stickers on her chest, Rio de Janeiro resident Ana Maria Vieira said she was certain to vote for the president, and would never countenance picking Lula.

"I saw what Lula and his criminal gang did to this country," she said, as she arrived to vote in Rio's Copacabana neighborhood, adding that she thought Bolsonaro's handling of the economy had been "fantastic."

Bolsonaro outperformed opinion polls in the first round on Oct. 2 among a field of 11 candidates. Pollsters said they recalibrated their methods based on that result.

A Lula victory would mark a stunning comeback for the leftist leader, who was jailed in 2018 for 19 months on bribery convictions that the Supreme Court overturned last year, clearing the way for him to seek a third presidential term.

In Sao Paulo, 31-year-old lawyer Gerardo Maiar said he was horrified by what Bolsonaro had done as president.

"The last four years were an embarrassment, both nationally and internationally," he said after voting. "I think it's ridiculous for Brazil to be in this shameful position."