A new poll ahead of Brazil's presidential election in October shows former president Luiz Inacio Lula da Silva maintaining a significant lead over Jair Bolsonaro, but the right-wing incumbent is gaining ground.

Forty-seven percent of those surveyed by the Datafolha consulting firm said they intended to vote for Lula, the 76-year-old leftist leader, in the first round election on October 2, the same result as last month's poll.

That represents a 15-point lead over the far-right Bolsonaro (32 percent), which is slightly narrower than the 18-point gap last month, but a significant jump over the 21-point spread in May.

If the election does advance to a second round, on October 30, the poll shows Lula beating Bolsonaro with 54 percent of the vote.