Lee was stabbed on the left side of his neck with a weapon by an unidentified man while touring the site of a proposed airport in Busan, Yonhap said.
The assailant was subdued and arrested at the scene, Yonhap said.
News photographs published showed Lee lying on the ground with his eyes closed and hands of other people around him pressing a handkerchief against the side of his neck.
Lee has been transported to a hospital, Yonhap said.
(Reporting by Hyonhee Shin; Editing by Sonali Paul and Neil Fullick)
