North Korean president Kim Jong Un and his southern counterpart Moon Jae have greeted each other in the Demilitarised Zone for a historic summit in the strip of land that divides their countries.

The meeting on the southern side of the truce village of Panmunjom, only the third since the end of the 1950-53 Korean War, will be the highest-level encounter yet in a whirlwind of nuclear diplomacy, and is intended to pave the way for a much-anticipated meeting between the North Korean leader and US President Donald Trump.

In the most detailed direct reference to the process by the North so far, the official KCNA news agency said Kim will "open-heartedly discuss all the issues arising in improving inter-Korean relations and achieving peace, prosperity and reunification of the Korean peninsula".

Moon, whose motorcade was seen leaving Seoul shortly after 8am, greeted Kim at the concrete blocks that mark the border between the two Koreas in the Demilitarised Zone to begin the rare occasion laden with symbolism. Talks are due to begin at 10.30am local time.

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"I am happy to meet you," Moon said. Moon also briefly stepped into the North before walking back.

When Kim stepped over the line about 9.30am, he became the first North Korean leader to set foot in the South since the Korean War ended 65 years ago.

Nuclear weapons will top the agenda, and today's summit will be the clearest sign yet of whether it's possible to peacefully negotiate those weapons away from a country that has spent decades doggedly building bombs despite crippling sanctions and near-constant international opprobrium.

Expectations are generally low, given that past so-called breakthroughs on North Korea's weapons have collapsed amid acrimonious charges of cheating and bad faith.

Sceptics of engagement have long said that the North often turns to interminable rounds of diplomacy to ease the pain of sanctions - giving it time to perfect its weapons and win aid for unfulfilled nuclear promises.

Advocates of engagement say the only way to get a deal is to do what the two Koreas will try at the summit: sit down and see what's possible.