As he landed at Pyongyang's Sunan International Airport on Tuesday morning, Moon was greeted by Kim, his wife Ri Sol Ju and other top North Korean officials, as well as a large honour guard and a military band.
Moon will hold at least two rounds of talks with Kim and try to convince him to carry out substantive steps towards disarmament that he can present to Trump when he meets him later this month on the sidelines of the UN General Assembly in NY.
Business leaders are there to underline the potential economic rewards for North Korea should it denuclearize, although deals can't be made unless and until US -led sanctions are lifted.
South Korea will be seeking to cement a breakthrough in faltering nuclear talks between Pyongyang and Washington.
"I will make special efforts on two issues at the upcoming summit to help establish lasting peace between the South and the North", he said.
U.S. President Donald Trump and the North Korean leader held the first-ever U.S.
More ambitious is Moon's attempt to unlock an impasse between Pyongyang and Washington over who should make the next move in their dialogue over peace and denuclearization.
The South Korean president now appears to be gambling he can revive the stalled nuclear talks and his own popularity at the same time.
North Korea says it has destroyed its main nuclear and missile engine test site and has halted atomic and ballistic missile tests, but US officials and analysts believe it is continuing to work on its weapons plans covertly.
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While it is still uncertain whether the U.S. would accept the idea of "declaration-for-declaration exchange", Kim of Kyungnam University said it would help to have North Korea and the USA "almost simultaneously declare" North Korea's nuclear arsenal and the end of the Korean War.
Moon will return home on Thursday.
Asan Institute for Political Studies Visiting Research Fellow Cheon Seong Whun told VOA, "It's not crystal clear that Kim Jong Un and [the] North Korean regime is willing to give up all those nuclear weapons and programs". While signalling his willingness to talk with Washington, Kim's strategy has been to try to elbow the USA away from Seoul so that the two Koreas can take the lead in deciding how to bring peace and stability to their peninsula.
Before his departure from Seoul, Moon said he meant to push for "irreversible, permanent peace" and for better dialogue between Pyongyang and Washington.
The first visit by a South Korean leader to Pyongyang in a decade is also the men's third meeting this year after two previous summits in April and May in the Demilitarized Zone that divides the peninsula.
While North Korea claims it has destroyed its main nuclear test site and stopped its missile tests, U.S. experts believe the country continues to develop weapons in secret.
North Korea's state-run media reported early Tuesday that Moon was to begin a visit, but said little else.
North Korea maintains that it has developed its nuclear weapons to the point that it can now defend itself against a potential United States attack, and can now shift its focus to economic development and improved ties with the South. (Yonhap) Im Jong-seok, President Moon Jae-in's chief of staff, announces the list of the entourage for Moon's trip to Pyongyang at Cheong Wa Dae on September 16, 2018. Kim Yo Jong, Kim Jong Un's sister and close aide, and North Korea's ceremonial head of state Kim Yong Nam were also present at the airport. Both meetings were held at the border village of Panmunjom. If all goes well the summit between President Moon and Kim Jong-un will produce a clarifying moment on the intentions of the rogue state and its promises to work towards scrapping its nuclear arsenal. Those trips produced a slew of inter-Korean rapprochement projects, which were suspended after conservatives took power in Seoul.