South Korean opposition leader Lee Jae-myung has been stabbed in the neck during a visit to the southern city of Busan and airlifted to hospital.
Lee, who narrowly lost the 2022 presidential election, underwent surgery at Seoul National University Hospital and was in an intensive care unit recovering and conscious, party spokesman Kwon Chil-seung told reporters.
He condemned the attack as "political terror".
The suspect, wearing a paper crown with Lee's name on it, approached and asked for an autograph as Lee spoke among a throng of supporters and reporters. He then lunged forward and attacked him, video footage showed.
Television footage and a video clip on the social media platform X showed the man lunging with his arm stretched out and stabbing Lee in the neck, the force of the attack pushing Lee back into the crowd behind him.
Lee grimaced and collapsed to the ground.
News photographs showed Lee lying on the ground with his eyes closed and bleeding, and people pressing a handkerchief against his neck.
Busan police official Son Je-han told a news briefing the assailant was born in 1957 and used an 18cm knife bought online. He did not identify the suspect and said the motive was being investigated.
Police will seek a charge of attempted murder, media said.
Jin Jeong-hwa, a Lee supporter who was at the scene livestreaming the event, told Reuters there were two dozen police officers present.
The assailant was quickly subdued by men including police officers, the footage showed.
President Yoon Suk Yeol condemned the attack and instructed best care be given, his office said.
"This type of violence must never be tolerated under any circumstances," his office quoted Yoon as saying.
A former governor of Gyeonggi province, Lee narrowly lost to conservative Yoon, a former chief prosecutor, in the 2022 presidential election. He has led the main opposition party since August 2022.
Lee is currently on trial for alleged bribery stemming from a development project when he was mayor of Seongnam near Seoul. He has denied any wrongdoing.
South Korea's next parliamentary elections are slated for April.
Lee's predecessor, Song Young-gil, was attacked in 2022 at a public event by an assailant who swung a blunt object against his head, causing a laceration.
Then conservative opposition party leader Park Geun-hye, who later served as president, was stabbed at an event in 2006 and suffered a gash on her face that required surgery.
Her father, Park Chung-hee, who was president for 16 years after taking power in a military coup, was shot and killed by his disgruntled spy chief in 1979 at a drunken private dinner.
In 2015, then-US ambassador to South Korea, Mark Lippert, was attacked by an assailant while attending a public event, suffering a large gash on his face.
