(CNN) Brazil's far-right presidential front-runner Jair Bolsonaro is recovering in a hospital after being stabbed during a rally while campaigning weeks ahead of elections.
"I'm fine and recovering!" Bolsonaro tweeted Friday from his hospital bed.
The candidate's son said Bolsonaro will likely be unable to resume campaigning ahead of October's vote, but that supporters can.
An assailant stabbed Bolsonaro on Thursday as he was led through a crowd on the shoulders of supporters in Juiz de Fora, a city in the southern state of Minas Gerais. Video shows Bolsonaro grimacing in pain before being carried away.
Police arrested Adelio Bispo de Oliveira, 40, who has been charged in connection with the attack, according to state news agency Agencia Brasil. The suspect's Facebook page featured posts railing against Bolsonaro, Agencia Brasil quoted police as saying.
Known to many of his countrymen as the "Brazilian Trump," Bolsonaro, 63, was taken to a local hospital, where medical officials and his family said he was in a stable condition.
The attack on Bolsonaro, notorious for making racist, sexist and homophobic remarks, has ratcheted up tensions weeks ahead of the elections.
A pro-gun congressman since 1991, he has cast himself as a political outsider, a firebrand attracting millions of supporters who believe he can shake up Brazil's corruption-marred political class.
Recent polls estimate that Bolsonaro is the favorite to win the election, with a 10% lead over his nearest rival, former President Luiz Inacio Lula da Silva.
However, doctors at the Santa Casa hospital, where Bolsonaro was taken for surgery, said his wounds may interrupt his campaigning as his recovery may take days or weeks.
His family initially thought his wounds were superficial, but later members said they had feared for his life.
"Unfortunately, it was more serious than we hoped," his son Flavio Bolsonaro tweeted. "The wound reached part of his liver, lung and intestine. He lost a lot of blood, reaching the hospital...almost dead...his condition now seems stable. Please pray!"
Another son, Eduardo Bolsonaro, said his father could have died if the hospital had not been nearby.
Flavio Bolsonaro later thanked supporters for their help, posting a photo of his father in a hospital bed, smiling and signaling a thumbs-up. "Jair Bolsonaro is stronger than ever and ready to be elected President of Brazil," he tweeted.
On Friday, Flavio Bolsonaro said his father was having some difficulty speaking. "He probably won't be able to go out onto the streets in this campaign. He can't go out onto the streets, but we can."
Doctors said they found internal bleeding and lacerations to the small and large intestines and not his liver. Bolsonaro may have to undergo another round of surgery in the coming months.
Bolsanaro is using a colostomy bag, and it will stay in place for at least two months, doctors said. He has been transferred to the Albert Einstein hospital in Sao Paulo, TV images and video showed.
In a longer tweet Friday, the candidate thanked family and supporters for their concern.
"Thank you from the bottom of my heart to God, my wife and children, who are by my side, to the doctors who are taking care of me and who are essential so that I could continue with you here on earth, and to all for the support and prayers!"
Human Rights Watch condemned the attack.
"Political or ideological differences should only be resolved through democratic processes, and never through violence," the watchdog group said in a statement. "The Brazilian authorities should carry out a prompt, impartial and thorough investigation into this crime, and ensure that justice is served."
The country has been wracked with violence and strikes that have buffeted the government of Michel Temer, who replaced Dilma Rousseff as Brazil's President after she was impeached in 2016.
A massive corruption scandal and economic woes prompted Brazilians to call for their own version of Trump, CNN reported last year.
Running for the small Social Liberal Party, Bolsonaro has seen his popularity surge as Brazil struggles to emerge from its worst recession, with the left and right heavily polarized, and the jailed Lula da Silva barred from office after failing to overturn a corruption conviction.
Lula da Silva has been in jail since April after he was sentenced to 12 years for corruption and money laundering. The accusations against him emerged after he left office in 2011.
The 72-year-old has strongly denied any wrongdoing. His defense said he was a victim of political persecution.
Lula da Silva's likely replacement as his party's presidential candidate, Fernando Haddad, tweeted that he "repudiated any act of violence" and wished Bolsonaro a speedy recovery.
In March, Marielle Franco, a Rio de Janeiro councilwoman and a prominent critic of police killings in shantytowns, was assassinated. Thousands in Brazil and across the world protested that killing.
Correction: This story has been updated to correct the spelling of the state where Bolsonaro was attacked.