Brazil's presidential frontrunners, right-wing populist Jair Bolsonaro and his left-leaning rival Fernando Haddad, are expected to face off in a run-off later this month, according to preliminary results.

The candidate for the Presidency of the Republic by the PSL, Jair Bolsonaro, arrives in the electoral section to vote on the elections of the first round, located in the Vila Militar, Rio de Janeir. [Photo: IC]

With 96 percent of the votes counted, Bolsonaro garnered 46.66 percent while Haddad secured 28.43 percent, according to results from the top electoral body Superior Electoral Court (TSE).

Center-left candidate Ciro Gomes came in third with 12.52 percent of the votes, compared with 4.83 percent for Geraldo Alckmin of the Brazilian Social Democracy Party (PSDB).

Voter turnout was 79.67 percent, or more than 112 million out of some 147 million eligible voters cast their ballots, leaving the abstention rate at 20.33 percent. Voting is mandatory in Brazil.

Some 91.22 percent of the votes cast were valid, while 2.67 percent of the ballots were left blank and 6.11 percent were nullified.