UPDATE 3-Brazil far-right candidate Bolsonaro stabbed while campaigning

Flavio Bolsonaro, the candidate's son, wrote on his verified Twitter account that "sadly, it was more serious that we had hoped for."

Brazil's front-running far-right presidential candidate Jair Bolsonaro was stabbed in the abdomen while campaigning on Thursday, and is in serious condition and undergoing surgery, his son and a hospital spokeswoman said.

Flavio Bolsonaro, the candidate's son, wrote on his verified Twitter account that "sadly, it was more serious that we had hoped for."

"The perforation reached part of his liver, lung, and intestine," Flavio Bolsonaro wrote. "He lost a lot of blood, arrived at the hospital ... almost dead. He appears to have stabilized now. Please pray!"

A hospital spokeswoman confirmed to Reuters that Bolsonaro was undergoing surgery but provided no details on his state nor his wounds.

Police in Minas Gerais state, where Bolsonaro was attacked, told Reuters they detained a man at the scene. They did not identify the suspect.

Globo TV showed images of Bolsonaro atop the shoulders of supporters in the midst of a crowd in the city of Juiz de Fora when he was stabbed.

Bolsonaro screamed in pain, then fell backward into the arms of those around him. It took a few moments for the crowd to realize what occurred, but they quickly rushed the candidate out of the street.

Bolsonaro, who has spent nearly three decades in Congress, is a law-and-order candidate who routinely says that Brazilian police should kill suspected drug traffickers and other criminals at will. 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.

Fernando Haddad, who will likely be the leftist Workers Party presidential candidate, said the stabbing was a "shame" and a "horror." Presidential rival Ciro Gomes also expressed outrage at the political violence.

Next month's election is the most unpredictable since Brazil's return to democracy three decades ago. Political corruption investigations have jailed scores of powerful businessmen, politicians and alienated voters who are infuriated with their representatives.