Kim crossed backed into North Korea, while Trump rejoined South Korean President Moon Jae-In for a press briefing.

President Trump and Kim Jong Un thanked each other for a private meeting in the demilitarised zone separating the two Koreas.

"It's just an honor to be with you and it was an honor that you asked me to step over that line and I was proud to step over the line... I enjoyed being with you and thank you very much," Trump concluded.

They met in the House of Freedom south of the demarcation line.

Kim called Trump crossing into North Korea a courageous decision, while Trump thanked him for coming, saying he would have looked bad if the North Korean leader had not showed up.

"When I put out a social media notification, if he did not showed up the press was going to make me look very bad. So you made us both look good. I appreciate that," Trump said at a briefing following the meeting.

Trump said he had developed a "great relationship" with Kim and credited himself with transforming the inter-Korean relations after becoming president.

The meeting was attended by US Secretary of State Mike Pompeo, Treasury Secretary Steven Mnuchin, Trump's daughter Ivanka and his son-in-law and adviser Jared Kushner.