Jair Bolsonaro, the far-right candidate who is leading the polls in Brazil’s presidential race, is in a serious condition but out of danger after being stabbed while campaigning just a month before the election.

Bolsonaro was rushed to the Santa Casa de Misericórdia hospital in the town of Juiz de Fora, about 125 miles (200km) north of Rio de Janeiro after being stabbed by a man who rushed up to him while he was being carried on the shoulders of a supporter through the crowd.

“The trajectory of the wound provoked various injuries. Mr Jair Bolsonaro arrived in a very serious condition at hospital with low pressure due to blood loss,” Glaucio Souza, one of the surgeons who operated on the candidate.

The knife wound went deep, cutting a vein in his abdomen and causing two other injuries in his intestines, said another surgeon Luiz Borsato, in a press conference broadcast on the hospital’s Facebook page.

“The patient is now in intensive care. It is naturally a serious state because of the magnitude of the trauma but he is stable,” Borsato said. The doctor said Bolsonaro was now conscious and had recognised his sons. 

Bolsonaro’s son Flávio – himself a candidate for the Brazilian Senate - had initially described the wound as “only superficial”, but later said that the injuries were more serious, tweeting that the candidate arrived at the hospital “almost dead” after losing a lot of blood.

Borsato said Bolsonaro would be in hospital for at least a week or ten days.

“The surgery is very recent. It could take days, it could take weeks. We can’t know how we will evolve,” he said, adding that Bolsonaro had shown good progress in the first few hours.

Videos shared on social media showed the moment Bolsonaro was attacked as he was carried on the shoulders of supporters in Juiz de Fora.

Bolsonaro was waving to the crowd when he suddenly clutched his abdomen and cried out in pain before falling backwards into the arms of those around him. O Globo newspaper reported that he was wearing a bulletproof vest, but was wounded just below it.

A police spokesman confirmed that the alleged attacker – named as Adélio Bispo de Oliveira – was in custody. Local media said he was beaten up by Bolsonaro supporters.

The G1 news website printed a leaked extract from the suspect’s police interview in which he said he had been ordered by God to carry out the attack.

“The Minas Gerais police reacted rapidly. Uniformed officers who were there arrested the attacker,” said Major Flavio Santiago, a police spokesman.

Santiago said such attacks on high profile candidates were rare in Brazil. “The candidates in this political process of getting close to their public, they have their security, police are there,” he said. “In Brazil we don’t have the culture of this type of attack, where someone can break through security and attack a candidate.”

Yet political violence is on the increase in Brazil. In March, Marielle Franco, a Rio de Janeiro city councillor for the leftist Socialism and Freedom party was murdered along with her driver Anderson Gomes in a crime which has yet to be solved.

That same month, two buses in a campaign caravan for former president Luiz Inácio Lula da Silva were hit by gunshots. Lula was not with the convoy at the time.

In an especially unpredictable campaign, Bolsonaro has polarised opinion with his homophobic comments, calls for looser gun laws, attacks on the left and praise for Brazil's 1964-1985 military dictatorship, which tortured thousands of its opponents and executed hundreds more.

Bolsonaro faces trial before the supreme court for speech that prosecutors said incited hate and rape.

Yet rising violent crime, anger over repeated corruption scandals and an efficient social media operation have helped him build support, and he is second in the polls to ex-president Lula, who has been barred from running because of a criminal conviction for corruption although he continues to appeal.

Analysts said that the incident could feeds Bolsonaro’s narrative that Brazil is in chaos and needs a firm hand to steady it.

"Paulo Baía, a professor of political science at the Federal University of Rio de Janeiro, said the attack would further polarize the election campaign. “The attack strengthens Bolsonaro and practically guarantees him a place in the second round,” he said.

“The campaign will be about passion. Any candidate who tries to use rationale will not win voters,” Baía said. “The attack on Bolsonaro messes with all the political forces in the country, it is the most important event in the campaign from diverse points of view.”

But Bolsonaro may not be able to continue his intense campaigning rhythm, said General Augusto Heleno, a retired member of Brazil’s top brass who almost became his vice before his own PRP party vetoed the idea.

“He has to recover, the consequences were serious, the accident had a big risk,” Heleno told the Guardian. “He will not be able to campaign in the way he has been doing, in the arms of the people, on top of sound trucks, it will be difficult in the short term.”

Heleno described the attack as “an act of barbarity that hurts democracy” and said he hoped that attacks on the candidate by the Brazilian media would now end. Bolsonaro’s political rivals were also quick to denounce the attack.

Fernando Haddad, who is likely to replace Lula as the Workers party presidential candidate, said the stabbing was a “shame” and a “horror”.

“The violence against the candidate Jair Bolsonaro is inadmissible and is a double attack: against his physical integrity and against democracy,” said Marina Silva, an environmentalist and centrist candidate.

But Dilma Rousseff, Lula’s successor, provoked some anger when she suggested that Bolsonaro’s extremist views could have provoked the attack.

“When you plant hate, you harvest thunderstorms,” she said in an interview with the Folha de S Paulo newspaper.

During the Congress session that began Rousseff’s 2016 impeachment proceedings, Bolsonaro dedicated his vote in favour of her suspension to a notorious dictatorship-era torturer. Rousseff was a member of the armed resistance to military rule and was herself tortured.

Bolsonaro recently said that members of her Workers’ party should be shot.

The Guardian