South Korean opposition leader Lee Jae-myung was stabbed in the neck on Tuesday by an unidentified knife-wielding man during a visit to the southeastern city of Busan.

Busan’s emergency office said Lee was attacked as he visited the construction site of a new airport in the city. It said Lee, head of the main opposition Democratic Party, was conscious but his exact condition was unknown.

Lee slumped to the ground, where a person pressed a handkerchief to his neck to stop the bleeding. Videos circulated on social media showed the attacker, wearing a paper crown reading “I’m Lee Jae-myung,” being chased and tackled by several people. He was arrested on the spot.

A witness, Jin Jeong-hwa, told YTN Television that the attacker approached Lee, saying he was a supporter and wanted to get his autograph, and then suddenly took out a knife-like weapon and stabbed him in the neck. Jin said Lee bled a lot.

President Yoon Suk Yeol expressed deep concern about Lee’s health and ordered authorities to investigate the attack, saying such violence would not be tolerated, according to Yoon’s office.

Lee lost the 2022 presidential election to Yoon by a narrow margin.

Lee, a liberal former provincial governor, is known for his outspoken style. His supporters see him as an anti-elitist hero who could reform establishment politics, eradicate corruption and solve growing economic inequality. Critics view him as a dangerous populist who relies on stoking divisions and demonising his conservative opponents.

• An AP report