Brazil's fiery leftist former leader Luiz Inacio Lula da Silva and his right-wing rival planned dueling presidential campaign rallies Wednesday.
Lula's 10-day campaign tour through southern Brazil has already been targeted by opponents throwing stones and raw eggs at the buses -- and at the two-term former president while he spoke on stage.
The apparent gunshots late Tuesday further ramped up tension ahead of the tour's culminating rally in the city of Curitiba.
"Our convoy is being targeted by fascist groups," Lula tweeted after bullets allegedly hit two buses. No one was hurt in the incident.
Gleisi Hoffmann, leader of the Workers' Party, which Lula founded, said the incident should be investigated as a possible assassination attempt.
"We hope we will have security, that the national and state police, as well as the intelligence services, do their jobs so that we can rally in a peaceful and democratic way," she told AFP.
Adding to the fevered atmosphere around Lula -- who leads in polls for the October 7 election, despite having been sentenced to 12 years in prison for corruption -- his closest rival was also due to appear in Curitiba on Wednesday.
Jair Bolsonaro, a former army captain who praises Brazil's two-decade-long military dictatorship, was due to arrive in Curitiba by plane, with supporters expected to meet him at the airport.
Bolsonaro taunted Lula, whom he called a "bandit," saying they'd see "who can get the most people out on to the streets without paying them."
Another right-wing group, the Movement for a Free Brazil, was planning its own anti-Lula rally in the city, just a short distance from where Lula and his Workers' Party faithful were due to gather.
The red-shirted Lula is no stranger to political drama, but even by his standards these are tempestuous times.
When Lula left office at the start of 2011, he was Brazil's most popular president on record, having presided over a commodities-fueled economic boom and won plaudits for his social policies.
However, he also has high rejection ratings and is blamed by the right and many in the center for Brazil's slide into the mammoth "Car Wash" corruption scandal that has shaken the country over the last four years.
Although dozens of other top politicians, including current center-right President Michel Temer, have also been charged or convicted, right-wing opponents see Lula as the graft scandal's biggest culprit. On the left, Lula is seen as the victim of politicized judges.
On Monday, a court rejected Lula's latest appeal against a conviction that he took a luxury apartment as a bribe.
That leaves him depending on a Supreme Court decision expected on April 4 if he is to avoid being ordered to start his 12-year prison sentence, let alone run for president.
Even then, he faces another six corruption cases.
Despite the daunting legal situation, Lula is a runaway favorite in opinion polls, with around 35 percent of voter intentions, followed by Bolsonaro with around 17 percent.
A veteran right-wing congressman, Bolsonaro is running as an anti-politician, often taking a leaf out of US President Donald Trump's book.
He has praised torture under Brazil's military dictatorship, insulted gays and even told a fellow politician she wasn't "worth raping."
The more extreme Bolsonaro gets, the more it seems he thrills his angry supporters.
Analysts say Brazil should brace for the worst tempered, most unpredictable election since the end of the dictatorship in 1985.
"If the official campaign hasn't even begun and we're already at the stage of throwing eggs and stones, the risk is that the election will get out of control," wrote Eliane Cantanhede, a columnist with the Estado de S.Paulo newspaper, before the shooting report.