He was in serious but stable condition and would remain in intensive care for seven to 10 days, Borsato said.
In a short clip posted to Twitter, Bolsonaro can be seen being carried through a crowd before an unidentified person stabs him in the chest. He was carried by his supporters to a vehicle, clutching his side.
Bolsonaro, who is known as Brazil's Donald Trump, is in stable condition, according to his son, Flavio Bolsonaro.
His son Flavio Bolsonaro confirmed his father's injuries are serious, saying "the perforation reached part of the liver, the lung and the intestine loop". Nearly dead... His condition now seems stable.
Santiago said the attacker was identified as Adelio Bispo de Oliveira, and he was beaten up badly by Bolsonaro supporters after the attack.
Police did not give a motive, but one official said the man appeared to be mentally unstable.
Police say the suspect who has been arrested, claimed that he was acting on God's orders.
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The public's anger is partially responsible for making this year's campaign the most unpredictable in years for Brazil, and the attack could lead to another seismic shift.
The incident comes after a tumultuous period in Brazilian history that saw a president impeached 2 years ago and the still popular former president Luiz Inacio Lula da Silva jailed and barred from running in the election this year.
The polls suggest he will get the most votes in the first round of the October presidential elections if former President Luis Inácio Lula da Silva remains blocked from standing, but he is unlikely to win a run-off.
Presidential candidate Jair Bolsonaro is taken on the shoulders of a supporter moments before being stabbed during a campaign rally in Juiz de Fora, Brazil, Sept. 6, 2018. A medical team is evaluating whether Mr Bolsonaro can be transferred to another hospital in Sao Paulo. "'I think the left shot itself in the foot because with this attack they will end up electing Bolsonaro'".
Earlier this year, Marielle Franco, a Rio city councilwoman who was an outspoken critic of police violence against slum residents, was assassinated.
Bolsonaro, like Lula da Silva, is revered by some but despised by others, reflecting the stark political polarization now gripping the South American nation.
The former military captain and a member of a fringe nationalist Social Liberal Party (PSL), Bolsonaro is a controversial figure in the Brazilian politics, known for his criticism of gays and immigrants as well as sympathies towards Brazil's 1964-1985 military dictatorship.