South Korea's conservatives made another about-face on Saturday and reinstated their nominee, just hours after dropping him and reopening the nomination process as the divided party struggled for unity to challenge the liberal front-runner in a presidential election four weeks away.

People Power Party nominee Kim Moon-soo welcomed the decision, which was made after polling party members over whether to replace him with former Prime Minister Han Duck-soo, whose late entry into the race derailed the consensus over its candidate for the snap June 3 presidential vote.

"Now everything will fall into place," he said in a statement, promising to seek unity and build a "big tent" coalition to take on liberal Democratic Party's candidate, Lee Jae-myung, when campaigning officially begins on Monday.