The leader of the South Korean opposition party Lee Jae-myung was stabbed in the neck by an assailant in Busan on Tuesday.
Lee was surrounded by journalists and supporters at a construction site in the southern port city of Busan when a man, pretending to be his supporter, lunged and struck him in the neck, South Korean television channels showed.
He was bleeding but conscious as he was rushed to a local university hospital, the Yonhap news agency reported, before being flown to the capital Seoul for surgery, according to an official from his party.
Police were seen wrestling the assailant, who wore a hat with a pro-Lee slogan, to the ground. He was arrested at the scene, Yonhap reported.
Lee was "walking to his car while talking to reporters when the attacker asked for his autograph," a witness told local broadcaster YTN, adding that Lee was then struck with what "looked like a knife."
The 59-year-old was seen collapsing to the ground as people rushed to aid him, one of whom pressed a handkerchief on Lee's neck before emergency responders carried him to an ambulance.
"This is an act of terror against Lee and a serious threat to democracy that should never occur under any circumstances," Kwon Chil-seung, an MP from Lee's Democratic Party, told reporters outside the hospital in Busan.
Lee was later flown to the capital, where Kwon said he would undergo surgery at the Seoul National University Hospital.
Police in Busan said Lee suffered a "1-centimeter laceration on his neck" and that he "remains conscious and bleeding is minor," according to South Korean news outlet Chosun Ilbo.
The attacker has not stated his motive, according to police officials cited by Yonhap.
Lee lost in 2022 to conservative Yoon Suk Yeol in the tightest presidential race in South Korea's history.
Yoon expressed "deep concern over the safety of Lee Jae-myung upon hearing of the attack," his spokeswoman Kim Soo-kyung said.
"Yoon emphasized our society should never tolerate this kind of act of violence under any circumstances."
A former child factory worker who suffered an industrial accident as a teenage school drop-out, Lee rose to political stardom partly by playing up his rags-to-riches tale.
He is widely expected to run for president again in 2027, and recent polls have indicated that he remains a strong contender.
But Lee's bid for the top office has been overshadowed by a string of scandals.
He avoided arrest in September when a court dismissed a request from the prosecution for him to be taken into custody pending trial on various corruption charges.
Lee still faces trial on charges of bribery in connection with a firm that is suspected of illicitly transferring $8 million to North Korea.
He is also accused of breaching his duties, allegedly resulting in a loss of 20 billion won ($15 million) for a company owned by Seongnam city during his term as its mayor.
Lee has denied all allegations against him.
In August last year, he launched a hunger strike against what he called the Yoon government's "incompetent and violent" policies.
He was hospitalized because of fasting-related ailments after not eating for 19 days.
