Ri Son Gwon, chairman of Pyongyang's "Committee for the Peaceful Reunification of the Country" led the North Korean delegation while Unification Minister Cho Myoung-gyon represented Seoul. Official Chinese news reports said Kim agreed in talks with Xi to discuss denuclearization.
Another round of working-level talks next Wednesday will discuss issues including protocol and security.
South Korean officials, who announced the summit date yesterday after high-level talks with their North Korean counterparts, said the summit agenda would largely be the denuclearisation of the Korean peninsula and an improvement of inter-Korean relations.
"We're moving along very nicely with North Korea".
Yesterday's meeting was the first high-level dialogue between the two Koreas since the delegation returned from the North.
Greeting the South Korean officials at the North Korea-controlled Tongilgak building, Mr Ri said the past 80 days have been filled with "unprecedented historic events" between the rivals, referring to the Koreas resuming dialogue before the Winter Olympics in the South and the agreement on the summit.
There has been a pressing need for the denuclearisation of North Korea by Japan, the US, China and South Korea.
The renegotiated trade deal, announced this week, doubled to 50,000 the number of cars each USA automaker can sell in South Korea without meeting local safety standards.
The upcoming inter-Korean summit will likely serve as a critical venue for discussions to resolve the nuclear programme of Pyongyang, which it said has expressed willingness to abandon the programme in exchange for peace.
"Both sides agreed to prepare for (the summit) in a way that would allow honest and heartfelt discussions (between the leaders)". It was also the first time Kim had stepped out of North Korean soil since he took power in 2011.
A summit between North Korea's Kim and US President Donald Trump is also expected to take place by the end of May.
Amid that process, Kim sustained this week in China his first visit overseas and dialogued with president Xi Jinping on the events in the península and issues of bilateral interest.
Kim subdued those anxieties by reportedly assuring Xi that their meeting "will yield abundant fruits of DPRK-China friendship, and facilitate peace and stability on the Korean Peninsula".
China has always been the North's key diplomatic defender and provider of trade and aid, but relations have been strained by Pyongyang's weapons programmes, with Beijing showing a new willingness to implement United Nations sanctions against it.
North Korean leader Kim Jong Un shakes hands with the head of the Chinese Communist Party's global affairs department Song Tao as Kim's wife Ri Sol Ju looks on, on a train in Dandong, China, in this still image from video released by KRT.