The two contenders in Brazil’s bitterly contested presidential race have urged calm after a wave of attacks on journalists, activists and members of the LGBT community by supporters of far-right candidate Jair Bolsonaro including beatings, a knife attack and a murder.

Supporters of the former paratrooper – himself the victim of an assassination attempt last month – have also reportedly been targeted with violence.

But an investigation by independent journalism group Agência Publica found that an overwhelming majority of the violence was committed by supporters of Bolsonaro, who polls give a 16-point lead over his leftist opponent, Fernando Haddad, ahead of the second-round runoff on 28 October.

Agência Pública said bolsonaristas were behind 50 separate attacks since 30 September. In the same period, six Bolsonaro supporters were assaulted, the report found.

“There is a flowering of hate that I have never seen before,” said a reporter who was attacked by Bolsonaro supporters in the north-eastern city of Recife. “I am frightened because it could be anyone now.”

Voter frustration over spiraling violence and eye-watering corruption – as well as an explosion of inflammatory fake news – mean an unusually toxic atmosphere has enveloped this year’s election.

Activists say that online threats have soared since campaigning begin, while videos of soccer fans chanting “Bolsonaro will kill queers” have spread terror among LGBT people.

Several attacks were reported on Sunday, when Bolsonaro secured his resounding victory in the election’s first round.

The 40-year-old female reporter was assaulted at knifepoint as as she went to vote, when two Bolsonaro supporters spotted the journalist’s credentials hanging from her neck.

One of the men, who was waving a knife and wearing a T-shirt emblazoned with the candidate’s face, grabbed her arm and told her: “When my commander wins the election you lot in the press will die.”

“The other one said, ‘Let’s take her off and rape her,’ and the one with the knife, said, ‘No, ‘Let’s cut her,’” said the journalist, who asked to withhold her name because she received threats after reporting the attack.

A Brazilian reporter who was roughed up by Bolsonaro supporters in Recife Photograph: Sérgio Bernardo/JC Imagem

She was scratched with the knife across her face and arms, before the two men ran off when a passing motorist blasted her horn.

Hours later, in the coastal city of Salvador, Romualdo da Costa, 63, a master in the Afro-Brazilian martial art of capoeira, was stabbed to death after a row over politics, police said.

Da Costa had said he voted for Haddad while the man who stabbed him declared support for Bolsonaro, BBC Brasil reported.

Bolsonaro shrugged off the attacks. “A guy with my T-shirt goes too far. What has that got to do with me?” he told reporters on Wednesday. “I am not in control of the millions and millions of people who support me. The violence comes from the other side.”

Later he changed tack, tweeting that he did not want votes from “those who practice violence against people who don’t vote for me”.

Haddad also condemned the attacks. “We have to put an end to this violence,” he told reporters.

Agência Pública reported that one woman was arrested and left naked in a cell after police in São Paulo caught her spraying the anti-Bolsonaro slogan “Ele Não” (“Not him”) on a wall. Police officers overwhelmingly support Bolsonaro, who has promised to give them more leeway to shoot suspects.

Agência Pública also reported that a university professor in Bahia state was arrested after running over a man selling Bolsonaro T-shirts. His university denied the accusation and said that he knocked over a clothes rail in a rush to get away because he felt threatened after refusing to buy one.

The violent mood has played out on the internet in the form of social media threats, a tsunami of fake news, and an online game featuring a cartoon Bolsonaro who attacks feminists, leftists and political opponents.

Prosecutors have launched an investigation into the game, Bolsomito 2K18, whose description reads: “Defeat the communistic evils in this politically incorrect game and be the hero that will free the nation from misery.”

Fatima Arruda, 36, a black, LGBT Brazilian activist who lives in Germany and has 120,000 followers on her Facebook page, said threats against her have multiplied since the campaign began.

“I’m lucky I don’t live in Brazil. If I was there I think something bad would have happened to me,” she said.

Bolsonaro himself is notorious for repeatedly making homophobic and sexist comments – once saying he would rather a child of his died than turn out gay. In September last year he was ordered to pay a £10,000 ($13,000) fine by a Rio court for racist comments about black Brazilians but the ruling was overturned on appeal.

Crisnando Lima, 26, a gay design student in the city of Teresina said he was walking to his local supermarket on Sunday when two men grabbed him and said: “When Bolsonaro wins, we will start beating up gays.”

Brazil’s poisonous political climate was made apparent in March, when Marielle Franco, a gay, black Rio de Janeiro city councilor, was murdered along with her driver, in what investigators believe was a targeted assassination.

A week before the election, two candidates from Bolsonaro’s Social Liberal party, posed grinning with the broken remains of a replica street sign bearing Franco’s name, which had been hung outside Rio’s town hall by her supporters.

The two men were later elected to congress and Rio de Janeiro’s state legislature.

Meanwhile Franco’s sister Anielle, 34, has described how she was threatened by four men last week after picking up her two-year-old daughter from school. “Bullshit leftist,” they screamed at her, “get out of here, feminist.”

She told the Guardian that she had been previously threatened online, but never in person. “There were so many insults I couldn’t remember them all,” she said.