Brazilian presidential candidate Flavio Bolsonaro reacts to the preliminary results from the country's closely contested presidential runoff on Sunday, October 25.

The senator, eldest son of former President Jair Bolsonaro, is challenging incumbent Luiz Inacio Lula da Silva of the Workers' Party in a bitterly fought race for Brazil's top job.

Bolsonaro has campaigned on a tough-on-crime platform, promising to crack down on organised crime, cut taxes and public spending, and shrink the size of government.

Flavio Bolsonaro narrowly topped the first round on October 4, securing 47.03% of valid votes against Lula's 45.16%.

Opinion polls ahead of the runoff pointed to a nail-biting finish, with a recent PoderData survey putting Bolsonaro on 51% of valid voting intentions and Lula on 49%, leaving the two candidates statistically tied within the survey's margin of error.