The exit poll by three leading South Korean broadcasters puts Lee, candidate of the leftwing Democratic party, in first place with 51.7 per cent of the vote, well ahead of rival Kim Moon-soo, of the conservative People Power party, on 39.3 per cent in the first-past-the-post election.

The U.S. ally has been without a permanent leader since late last year, when then-President Yoon Suk Yeol was impeached over his botched declaration of martial law.

Kim Moon-soo's concession means Democratic Party candidate Lee Jae-myung has won the election to be South Korea's next leader. In a speech just concluded, Lee vowed to restore the country's economy and to make peace in the Korean peninsula.