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.
Trump said on Twitter that he will be speaking to Xi about later on Tuesday, adding that North Korea would be one of the topics they would talk about.
Regional powers and the United States are seeking to prevent North Korea from obtaining nuclear weapons.
For his part, Kim could be trying to improve ties with Xi - which have been frosty, to put it mildly - in case his outreach to Trump falls flat, analysts say.
Mr Kim is quoted as saying: "These are the positive outcomes of the historic meeting between me and Comrade General Secretary (Xi)".
"At this very moment, Secretary Pompeo is on his way to North Korea in preparation for my upcoming meeting with Kim Jong-un", Trump said.
China is likely trying to insert its interests into ongoing inter-Korean talks and shape Kim's message to President Donald Trump when the two meet. "Maybe North Korea and the USA are thinking about making some radical concessions".
Xi is said to have told Kim of his support for North Korea's strategic shift towards economic development.
Chinese President Xi Jinping and North Korean leader Kim Jong-un met surreptitiously for the second time in less than two months, a development which reflects growing proximity between the two countries ahead of Pyongyang ruler's crucial meet with US President Donald Trump this month.
China and North Korea fought side by side in the Korean War (1950-53), and remain close, but relations have been strained since the start of Pyongyang's nuclear programme, which Beijing fears has raised tensions on its borders.
Kim held a historic meeting last month with South Korean President Moon Jae-in, and Xi and Kim first met secretly in March.
China has been North Korea's only ally in the region though their relations took a nosedive of late over Pyongyang's reckless nuclear ambitions and also China's enforcing of the United Nation's sanctions imposed on the latter to curb its tests.
The South Korean government is exploring ways to increase economic cooperation with North Korea without breaching worldwide sanctions or earning the ire of Trump.
North Korean state media KCTV said Kim flew to Dalian on Monday on his private jet, where he was welcomed by high-profile Chinese officials including Foreign Minister Wang Yi.
It was not known how long the Xi-Kim meeting had been planned or why Dalian was chosen. Others claimed to have spotted Red Flag limousines used by the statesmen, AP said.