STORY: Brazilians cast their votes on Sunday in the country's most polarized election in decades.

Left-wing former president Luiz Inacio Lula da Silva, who has had a solid lead in opinion polls for months, is expected to beat far-right incumbent Jair Bolsonaro.

But the current president has said he may refuse to accept defeat and avoided answering questions from reporters on Sunday about whether he would respect the election's outcome.

"What is important are people’s voices and clean elections, without any problems. May the best one win."

Bolsonaro made baseless allegations of fraud, accusing electoral authorities of plotting against him and suggesting the military should conduct a parallel tally, which they declined to do.

Following Bolsonaro's criticisms of Brazil's voting systems, the national electoral authority invited a record number of foreign election observers to monitor the poll.

Lula acknowledged the dramatic turnaround in his fortunes after a conviction that he says was politically motivated, saying he wanted to help Brazil "return to normal.”

Brazilians are also voting on Sunday for all 513 members of the lower chamber of Congress, a third of the 81 members of the Senate as well as state governors and legislatures.