Brazilians target Bolsonaro poll threats

Brazilian business leaders, intellectuals and artists have gathered to defend democratic institutions after attacks by President Jair Bolsonaro that have raised fears he could reject the results of October's presidential election.

The far-right leader and former army captain has questioned Brazil's electronic voting system and attacked Supreme Court justices who oversee elections, accusing them without evidence of favouring his leftist rival, who leads in opinion polls.

Prominent Brazilians, from top bankers to union leaders, signed a manifesto organised by Sao Paulo's confederation of industries expressing support for the judiciary as it prepares for the October 2 election under fire from Bolsonaro.

They called the top court "the ultimate guardian of the constitution" and said the Superior Electoral Court has conducted the country's elections with total integrity.

Another manifesto, also read out to a cheering crowd at University of Sao Paulo's law school and signed by nearly a million people, warned the country's democracy was under threat.

"Out with Bolsonaro", the audience shouted after the manifesto called 'letter to the Brazilians' was read in the same place as a similar manifesto was read in 1977 to denounce Brazil's military dictatorship at the time.

The manifesto was signed by former President Luiz Inacio Lula da Silva, who is the frontrunner in the presidential race, although his advantage has narrowed in recent polls.

Bolsonaro, an admirer of Donald Trump who backed the then-US president's false claims of fraud in the 2020 election, ridiculed the manifesto, saying he had no need to sign a letter to prove his democratic credentials.

His opponents say he is preparing the ground to contest the election results if he loses, in the same way Trump has done since his 2020 defeat.

Several thousand demonstrators later marched along Sao Paulo's Paulista Avenue in support of democracy and chanting for Bolsonaro to stop threatening the voting system.

Similar demonstrations were planned by civil society organisations in other Brazilian cities.

"The purpose of the demonstrations is the defence of democracy ... against the threat of a coup," organiser Raimundo Bonfim, told Reuters.

Brazil's most polarised election in decades is expected to go to a second-round runoff between Bolsonaro and Lula on October 30 if neither candidate wins 50 per cent of valid votes on October 2.

The country's top newspapers cancelled a presidential debate planned for September 14 after the two main candidates did not confirm their participation.

Bolsonaro said he would only debate after the first round. Lula cited scheduling difficulties.