Brazilian presidential candidate Flavio Bolsonaro reacts to preliminary results from the country's general election on Sunday, October 4 in Rio de Janeiro.

Bolsonaro, a senator and eldest son of former President Jair Bolsonaro, is the main challenger to incumbent President Luiz Inacio Lula da Silva of the Workers' Party. He is campaigning on tougher measures against organized crime, tax and spending cuts and a smaller federal government.

Backed by his father, Bolsonaro also supports an amnesty that could benefit the former president and others convicted over efforts to overturn the 2022 election result. Jair Bolsonaro is serving a 27-year prison sentence over a failed coup plot and is barred from holding public office.

If no candidate wins more than 50 per cent of valid votes, the two leading candidates advance to a runoff on October 25.