Brazilian President Luiz Inacio Lula da Silva reacts to the preliminary results from the country's closely contested presidential runoff in Sao Paulo on Sunday, October 25.

Lula is fighting for a fourth non-consecutive term against Senator Flavio Bolsonaro, the eldest son of former President Jair Bolsonaro, in a race that remains on a knife-edge.

The Workers' Party candidate has campaigned on strengthening workers' rights, improving living standards and expanding social programmes.

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%, within the survey's margin of error.