South Korea's opposition leader, Lee Jae-myung, was stabbed in the neck during a visit to Busan, according to local media.
The city's emergency office said the man was attacked while touring a construction site at a new airport.
She added that Lee, who heads the main opposition Democratic Party, was conscious but his exact condition was not known.
A party official said he was taken to a local university hospital.
An unidentified man reportedly approached the politician to get his autograph before lunging in with a knife-like weapon South KoreaYonhap News Agency.
Yonhap said the man, who appeared to be in his 50s or 60s, was quickly restrained and arrested.
YTN TV images showed Lee scowling and collapsing on the floor, and other images showed people pressing a handkerchief to the side of his neck.
Lee was taken away on a stretcher. Photo: AP
He said he had a wound about 1 cm long.
Lee lost the 2022 presidential election to Yoon Suk-yeol by a narrow margin.
He is currently on trial for alleged bribery – which he denies – in connection with a development project when he was mayor of Seongnam near Seoul.
The liberal is also known for his outspoken style, with supporters viewing him as an anti-elite crusader, but critics viewing him as a populist who stokes divisions and demonizes conservative rivals.
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He was the politician in the southern port city of Busan
A spokesman for President Yoon Suk-yul condemned the attack and expressed deep concern about Lee's condition.
South Korea has strict gun laws, but there is a history of political violence using other weapons.
Lee's predecessor, Song Young-gil, suffered a head injury when he was attacked with a sharp object at a public event in 2022.
