Mr Kim joked during the summit that he would no longer interrupt his counterpart’s sleep with early morning missile tests as the two leaders held talks on denuclearisation and other issues in Panmunjom, in the demilitarised zone.
The North Korean’s pre-planned crossing into the south was historic – the first by a regime leader in more than half a century – but it was Mr Moon’s unplanned step over the border that took observers by surprise.
As the pair shook hands on the southern side, Mr Moon asked Mr Kim: “You have crossed into the South, but when do I get to go across?”
Footage of the meeting showed his hesitant reaction as the North Korean leader replied: “Why don’t we go across now?”
Hand-in-hand they stepped briefly into North Korea before continuing southward shortly after 9.30am local time.
The border crossings made the summit a “landmark event”, said Colin Alexander, a political communications expert from Nottingham Trent University.
He added: “North Korean propaganda claims that the South is a puppet under the control of the US.
“Thus, North Korean military personnel refer to the other side of the border as the ‘American side’. We should not underestimate the significance of a North Korean leader being prepared to step over the line into ‘American’ territory.”
During their private meeting on Friday, Mr Kim told Mr Moon he had come to the summit to end the history of conflict between the countries, a South Korean official said.
He added he would be willing to visit the presidential Blue House in Seoul, invited Mr Moon to Pyongyang, and said he wanted to meet “more often” in future, the official added.
But there is widespread scepticism about whether Mr Kim is ready to abandon the nuclear arsenal his country has defended and developed for decades, as what it calls a deterrent against US invasion.
Two previous summits between the leaders of North and South Korea, in Pyongyang in 2000 and 2007, failed to end the North’s weapons programmes or improve relations in a permanent way.
“Today, rather than create results we won’t be able to carry out like in the past, we should make good results by talking frankly about current issues, issues of interest,” Mr Kim said.
On Friday afternoon, the leaders issued a joint declaration to say that North and South Korea would begin talks with a view to signing a peace treaty to formally end the Korean War later this year, 65 years after hostilities ended.
Their encounter came just weeks before Mr Kim is expected to meet with Donald Trump, when the US president plans to make a further push for denuclearisation.
Experts have warned the two sides may have differing ideas about what that means, however.
And Mr Kim’s declaration that he would end nuclear weapons testing was followed by claims the North’s main test site at Punggye-ri under Mount Mantap had collapsed.
Chinese scientists studied a series of earthquakes after Pyongyang’s latest and most powerful experiment, which they believed were caused by collapsing earth.
The White House said in a statement on Friday it was ”hopeful that talks will achieve progress toward a future of peace and prosperity for the entire Korean peninsula ... [and] looks forward to continuing robust discussions in preparation for the planned meeting between president Donald J Trump and Kim Jong-un in the coming weeks”.
And UK Foreign Secretary Boris Johnson, speaking at Nato headquarters, told reporters he was “very encouraged” by the summit, but added: “I don’t think that anybody looking at the history of North Korea’s plans to develop a nuclear weapon would want to be over-optimistic at this point.
“But it is clearly good news that the two leaders are meeting.”
China, North Korea’s sole major ally, also welcomed the meeting. A foreign ministry spokeswoman said it was a chance to expand into a “new journey of long-term peace and stability on the peninsula”.
Additional reporting by agencies
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