Kim's special train departed Beijing Wednesday afternoon and headed towards the northeast border, where it will enter North Korea early Thursday morning.
North Korea will "make efforts for the second summit between (North Korean) and US leaders to achieve results that will be welcomed by the worldwide community", Kim was quoted as saying by China's official Xinhua News Agency.
Analysts say China could use the North Korean issue as a bargaining chip in the negotiations, but Beijing's foreign ministry rejected any link between Kim's trip and the talks.
Shi Yinhong, an global relations professor at Renmin University in Beijing, said Kim's trip would have no direct influence on the progress of trade talks.
There has been no mention of the meetings so far in Chinese or North Korean state media.
Kim's trip to China - his fourth in the past 10 months - is believed to be an effort to co-ordinate with Beijing ahead of a possible second summit with Trump. But talks have since stalled over disagreements about how to accomplish that.
Wang Yiwei, a senior research fellow at the Center for China and Globalization, said he believed North Korea was becoming impatient and beginning to lose hope with the United States for asking it to make changes without in turn removing sanctions.
China's official Xinhua news agency confirmed that Kim was visiting from Monday to Thursday at Xi's invitation.
Xi commended North Korea for its denuclearisation efforts and said China supported the resolution of concerns through dialogue.
Kim has previously said his country has completed the development of its nuclear arsenal and Pyongyang has rejected demands for what it calls its "unilateral" disarmament as "gangster-like".
Kim spoke with Xi for about an hour Tuesday night, discussing ways to strengthen their ties and lay out strategy for a potential summit between Kim and Trump on curbing Pyongyang's nuclear ambitions, Yonhap reported, citing unidentified people familiar with the talks.
Yonhap said Kim met with President Xi Jinping for about an hour on Tuesday and later attended a dinner at the Great Hall of the People in central Beijing hosted by Xi and his wife, Peng Liyuan.
Kim said in his New Year speech he was ready to meet Trump any time to achieve their common goal of denuclearisation of the Korean peninsula.
Chinese Foreign Ministry spokesman Lu Kang would not comment on the goal or timing of Kim's visit at a briefing Tuesday, saying only that the two countries were making "joint efforts to uphold peace and stability on the Korean peninsula".
"China has always supported both sides to continue to hold talks and to reach a positive outcome", Lu said.
Officially, at least, China says it considers the tariff battle and North Korea's weapons programs to be entirely separate.
Kim's visit also comes after he expressed frustration in his annual New Year's address over the lack of progress in negotiations with Washington since the Singapore summit with Trump in June, saying that if things don't improve - meaning that if sanctions relief and security guarantees aren't in the offing -Pyongyang might have to find "a new way" forward.