Lee Jae-myung at a hospital after being stabbed in Seoul, South Korea, on Tuesday. Reuters

An unidentified knife-wielding man stabbed South Korea’s tough-speaking liberal opposition leader, Lee Jae-myung, in the neck during a visit Tuesday to the southeastern city of Busan, police said.

Lee, 59, the head of the main opposition Democratic Party, was airlifted to a Seoul hospital for surgery after receiving emergency treatment in Busan. Police and emergency officials earlier said he was conscious after the attack and wasn’t in critical condition, but his exact status was unknown.

The attack happened as Lee walked through a crowd of journalists and others after a tour of the proposed site of a new airport in Busan. The attacker approached Lee, saying he wanted to get his autograph, and then stabbed him in the left side of his neck with a knife, senior Busan police officer Sohn Jae-han said in a televised briefing.

Sohn said Democratic Party officials near Lee quickly subdued the attacker before police officers detained him. He said 41 police officers had been deployed to the area for crowd control and traffic management.

TV footage showed Lee, his eyes closed, lying on the ground as a person pressed a handkerchief to his neck to stop the bleeding. A witness, Jin Jeong-hwa, told YTN television that Lee had bled a lot. Videos circulated on social media showed the suspect, wearing a paper crown reading "I’m Lee Jae-myung,” being chased and tackled by several people, apparently including plainclothes police officers.

South Korean opposition leader Lee Jae-myung lies on a stretcher a heliport in Seoul, South Korea. AP

Sohn said the suspect, aged about 67, told investigators that he bought the 18-centimeter (7-inch) knife online. He said police are investigating the motive for the attack.

Lee’s Democratic Party called the incident "a terrorist attack on Lee and a serious threat to democracy.” It called on police to make a through, swift investigation.

At Pusan National University Hospital in Busan, where Lee received emergency treatment, party spokesperson Kwon Chil-seung said Lee’s jugular vein was believed to have been damaged and there was concern over the large amount of bleeding. Hospital officials would not comment on Lee’s condition.

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.

Associated Press