Chinese media said Kim met with Xi on Monday and Tuesday. As with the previous Xi-Kim meeting, there was no advance notice given, and the visit was only confirmed after Kim had left.
U.S. President Donald Trump said he will discuss trade with Chinese President Xi Jinping on Tuesday, as both sides continue talks after failing to reach a consensus at talks in Beijing last week, Reuters reports.
This is their second meeting after their first secret one in Beijing in late March.
"As long as relevant parties abolish their hostile policies and remove security threats against the DPRK, there is no need for the DPRK to be a nuclear state and denuclearization can be realized", Xinhua quoted Kim as telling Xi.
Shortly after the news of Kim-Xi summit in Dalian, Trump said he would speak with Xi on North Korea.
In an unprecedented meeting at the demilitarized zone separating the two countries, Kim became the first North Korean leader to step into South Korean territory since 1953.More news: Instagram quietly launches payments feature
The South Korean government is exploring ways to increase economic cooperation with North Korea without breaching global sanctions or earning the ire of Trump. A status quo, it's worth noting, that means that the decades-long U.S. military presence in Korea will remain for decades more to come. The North is now detaining three USA prisoners, and early talks before the summit strongly inferred that the prisoners would be released as a deed of "good will", according to inside White House source Rudy Giuliani.
NHK television showed images of two planes taking off from the northeastern port city of Dalian, one belonging to North Korea's Air Koryo, and another used by high-profile officials from Pyongyang.
China is North Korea's only major ally, although trade has plummeted in recent months as Beijing enforces United Nations economic sanctions in response to the North's nuclear bomb and ballistic missile tests.
Kim said he had come to China to inform Xi of the situation, as events on the Korean Peninsula are unfolding rapidly.
Past trips by past North Korean leaders have also followed the pattern of being carried out quietly and only discussed after they are over.
Japan's Kyodo News service said the plane departed on Tuesday.
After their meeting, the leaders of North and South Korea signed an agreement to officially end the Korean War after 65 years, which will be declared later this year, and to work to denuclearize and establish a nuclear-free Korean Peninsula.
Speculation about Kim's visit to China started when security in Dalian, located close to the China-North Korea border, was increased and Kim's private jet was spotted at the airport of Dalian.