BRASILIA, Aug. 8 (Xinhua) -- Brazil's ex-President Luiz Inacio Lula da Silva, presidential candidate of the Workers' Party (PT), leads a pre-election poll in the state of Sao Paulo on Wednesday.

The poll shows Lula has 21.8 percent support among voters in the state, which is the country's most populous.

According to polling firm MDA Institute, Jair Bolsonaro of the conservative Social Liberal Party, is in second place with 18.4 percent, followed by the ex-Governor of Sao Paulo, Geraldo Alckmin of the Social Democracy Party, with 14 percent.

Ex-Minister of the environment Marina Silva, of the Sustainability Network, had 6.7 percent support, slightly more than ex-Minister of national integration Ciro Gomes of the Democratic Labor Party, who had 5 percent.

The number of undecided voters increased to 26.8 percent with only two months to go before the Oct. 7 vote.

The poll also found that 50.4 percent of voters said they had little or no interest in the elections, while 21.7 percent were very interested.

Lula continues to be the favorite to win despite being behind bars, serving a 12-year sentence for corruption. He denies any wrongdoing and supporters say the trial aimed to prevent his reelection.

He is likely to be disqualified from running by the electoral court, since Brazilian law bars anyone convicted of a crime from running for elected office, but the PT said it plans to register him anyway.

The party has also chosen a backup candidate, ex-Minister of education and ex-Mayor of the city of Sao Paulo, Fernando Haddad.

With Lula out of the scenario, Bolsonaro's lead widens slightly to 18.9 percent, followed by Alckmin with 15 percent.

The pollster surveyed 2,002 registered voters between August 2 and 5 across 75 cities in Sao Paulo.

The poll has a margin of error of 2.2 percentage points and a 95 percent accuracy rate.