Brazilians are voting on October 4 in the first round of the presidential election, a tight race between incumbent Luiz Inacio Lula da Silva and Flavio Bolsonaro. Polls open at 8 am local time and close at 5 pm.

Final polls put Lula at about 40 to 45 per cent of valid votes and Flavio Bolsonaro at 36 to 42 per cent, with Datafolha giving 45 per cent to 40 per cent. Other candidates trail far behind in single digits.

Under Brazilian law, a candidate needs more than 50 per cent of valid votes to win in the first round. With the gap narrow and minor candidates siphoning votes, a runoff looks likely. A runoff would follow weeks later.

The second-round picture is even tighter. Poll aggregators show a statistical tie, with second-round voter transfers from eliminated candidates deciding the outcome.

About 158.7 million Brazilians are eligible to vote. Electronic voting machines deliver results fast: the country should know whether a runoff is needed within hours of polls closing.