The run-up to a presidential election in Brazil plunged into chaos on Friday after a knife attack on far-right candidate Jair Bolsonaro put the frontrunner in intensive care just a month before the vote.

Congressman Bolsonaro, who has enraged many Brazilians for years with controversial comments but has a devout following among conservative voters, could take two months to fully recover and will spend at least a week in hospital, said Dr. Luiz Henrique Borsato, who operated on the candidate.The attack on Bolsonaro, 63, is a twist in what was already Brazil's most unpredictable election since the country's return to democracy three decades ago. Corruption investigations have jailed scores of businessmen and politicians in recent years, and alienated voters.

There was fear of violence flaring across Brazil on Friday, as the nation celebrates Independence Day with political groups likely to march in hundreds of cities. Bolsonaro's rival candidates called off campaign activities for Friday.

Bolsonaro, whose trademark pose at rallies is a "guns up" gesture with both hands to make them resemble pistols, has said he would encourage police to kill suspected drug gang members and other armed criminals with abandon. He has openly praised Brazil's military dictatorship and in the past said it should have killed more people.

Bolsonaro faces trial before the Supreme Court for speech that prosecutors said incited hate and rape. He has called the charges politically motivated.

His stabbing is the latest instance of political violence, which is particularly rampant at local level. For instance, in the months before 2016 city council elections in Baixada Fluminense, a hardscrabble region the size of Denmark surrounding Rio de Janeiro, at least 13 politicians or candidates were murdered before ballots were cast. Earlier this year, Marielle Franco, a Rio city councilwoman who was an outspoken critic of police violence against slum residents, was assassinated. But violence is rare against national political figures, even in the extremely heated political climate that has engulfed Brazil in recent years.