Jair Bolsonaro with 10-point lead over Fernando

Brazil's far-right presidential candidate Jair Bolsonaro has a 10-point lead over leftist Workers Party candidate Fernando Haddad, and would tie in a second-round runoff against him this month, an opinion poll showed on Monday.

Bolsonaro, who is recovering from a near-fatal stabbing, has increased his lead ahead of the election this Sunday with 31 per cent of voter support in a simulated first-round ballot, the survey by polling firm Ibope said, while Haddad has 21 per cent.

In the likely case of a runoff vote, required if no candidate takes a majority, Bolsonaro and Haddad both had 42 per cent, with the remaining voters undecided or saying they would annul their ballots.