Some of Brazil’s most celebrated musicians, writers and public intellectuals have said Latin America’s largest democracy could take an authoritarian turn if rightwing populist Jair Bolsonaro emerges victorious from next month’s presidential election.

With less than a fortnight until the 7 October vote, Bolsonaro, a pro-torture former army captain who recently called for his political opponents to be shot, leads polls with about 28% of the vote.

Bolsonaro’s supporters, many of whom hail from Brazil’s middle and upper classes, see him as an iron-fisted antidote to the corruption and violence they believe is the result of 13 years of leftist Workers’ party rule.

But in an online manifesto that reflects mounting anxiety over a possible Bolsonaro presidency, 150 prominent artists and thinkers denounced him as “a clear threat to our fundamental civilisational heritage”. Signatories include Caetano Veloso, Chico Buarque and Gilberto Gil, a trio of politically engaged composers who all spent time in European exile during Brazil’s 1964-1985 dictatorship.

Gilberto Gil is one of the signatories. Photograph: AFP/Getty Images

“It’s never too often to remember how throughout history and to this day fascist, Nazi leaders and many other autocratic regimes were first elected with the promise of rescuing the self-esteem and credibility of their nations, before submitting them to the most varied authoritarian excesses,” said the declaration, Democracia sim or “yes to democracy”.

The signatories called themselves a politically mixed bag with a common commitment to a free, tolerant, inclusive and democratic Brazil. They also include: rapper Mano Brown from the group Racionais MC’s, the actor Camila Pitanga, the director Fernando Meirelles, the novelist Milton Hatoum, the feminist scriptwriter Antônia Pellegrino, and the doctor, writer and broadcaster Drauzio Varella.

The manifesto, which organisers say has attracted more than 180,000 signatures since being published on Monday, is the latest in a series of anti-Bolsonaro protests to emerge in the lead-up to Brazil’s most unpredictable and divisive election since the return of democracy in the 1980s.

Caetano Veloso is one of those who fears ‘authoritarian excesses’ under a Bolsonaro presidency. Photograph: Rafa Rivas/AFP/Getty Images

Millions of Brazilian women have joined a Facebook group created to try to derail his presidential bid and some of Brazil’s best-known female singers have lent their voices to a social media campaign that uses the hashtag #EleNão or #NotHim.

One anti-Bolsonaro samba circulating on social media features the lyric: “[Under Bolsonaro] we’ll have bullets, revolvers and grenades on our plates instead of rice and beans. Not him! Not him! Not him. For the love of God, not him! … If this chap gets elected and sees this video, I’m off to Japan. Not him! Not him! Not him. For the love of God, not him!”

Fears Bolsonaro could drag Brazil back into dictatorship are not confined to Brazil’s cultural and intellectual elite.

Juvenil Mendes, a 56-year-old taxi driver from the town of Teófilo Otoni in Minas Gerais state, estimated that 40% of his colleagues backed the far-right candidate because of his hardline stance on crime. But he felt they were making a grave mistake. “Today we’ve got these silly billies going around saying: ‘Let’s vote for Bolsonaro. Let’s have the military take back control of the country!’ They don’t know what they are talking about. They have no idea what a dictatorship is.”

Danrusssel Contão, a 27-year-old Bolsonaro supporter in the nearby city of Governador Valadares, rejected claims his candidate was an authoritarian. “I believe that when it comes to governing the country he won’t be a totalitarian, like everyone says,” said Contão, who helps run the campaign of a local candidate for Bolsonaro’s party, the Social Liberal party (PSL).

“He’s got a firm hand but I don’t think he’s a hard-line guy. He’s a humanitarian. He thinks about other people’s rights,” Contão added. “Brazil needs someone with the courage to fight for the people’s interests and the people’s rights.”