The other US participants are Secretary of State Mike Pompeo and acting chief of staff Mick Mulvaney. National Security Advisor John Bolton, known for his hawkish views on North Korea, is also in Hanoi for the summit but he has not been invited.

Kim will be accompanied by Kim Yong-chol, a top Workers' Party official who met Trump in Washington D.C., and an "as yet unknown third associate." The leader may bring his sister and key aide, Kim Yo-jong.

Kim and Trump are expected to start the warm-up meetings, exchanging pleasantries in a bid to demonstrate their budding chemistry. The mood is likely to serve as a litmus test of this week's summit results that may decide the future of the nascent peace process spearheaded by the showy leaders.

Full-fledged negotiations on core and sensitive summit agenda items are expected to take place on Thursday, the last day of their Hanoi session aimed at following up on their agreement reached at their first meeting in Singapore in June.

Senior nuclear envoys of the two sides are believed to have drafted a rough joint statement, while filling in some blanks on sensitive issues is up to the leaders' bargaining.

After checking into his hotel in Hanoi on Tuesday, Kim received a "detailed" briefing from his negotiators who had preliminary talks with US officials in recent days, Pyongyang's state news agency, the KCNA, reported.

Drawing keen attention is whether the leaders will reach meaningful agreements on the fate of the Yongbyon nuclear complex, the heart of North Korea's nuclear program, and other major facilities connected to its weapons of mass destruction development.

Trump's priority is to win a deal on freezing their operations.

A best-case scenario for the self-styled master negotiator is securing Kim's promise to shut down the Yongbyon compound in a verifiable and irreversible way, plus a timetable on full denuclearization.

Potential benefits for Pyongyang include a political end to the 1950-53 Korean War, which ended in an armistice, sanctions relief and the continued suspension of regular combined military exercises between the US and South Korea.

Trump signaled that time is on his side, repeatedly saying that he is "in no rush." He said the Hanoi meeting with Kim won't be the last, effectively lowering public expectations on the summit outcome this time.

Trump is scheduled to hold separate meetings with Vietnamese Communist Party General Secretary and President Nguyen Phu Trong and then meet Prime Minister Nguyen Xuan Phuc from 11 a.m.

Kim's pre-summit schedule remains unclear. He visited the North Korean Embassy in Hanoi on Tuesday evening.

Kim is likely to meet the Vietnamese leaders during his two-day "official goodwill" visit to the Southeast Asian nation to come on the heels of the summit with Trump. The Vietnamese government earlier announced Kim has a plan for what it called a "friendly official" trip but did not specify a date.

Kim plans to make the official visit on Friday and Saturday, the KCNA reported. (Yonhap)