Security is tight at the Sofitel Legend Metropole Hotel in Hanoi, where Trump and Kim will meet later today.
Earlier, Vietnamese officials greeted Kim at the station in Dong Dang town after he crossed the border from China by train.
The two sides have discussed specific and verifiable denuclearization measures, such as allowing inspectors to observe the dismantlement of North Korea's Yongbyon nuclear reactor, US and South Korean officials say.
Kim's bodyguards are picked for fitness, height, eyesight, marksmanship, martial arts prowess, and even their good looks, says the BBC's South Korea correspondent Laura Bicker.
Tottenham manager Mauricio Pochettino accepts FA charge, apologises to referee
Pochettino said games like that were must-win matches if they were to compete for top spot. My behaviour was public and now I want to apologise in a public way.
That would "probably be the last thing he needs" amid the possible release this week of a summary of the special counsel's report into ties between Russian Federation and Trump's 2016 election campaign, adds Carafano.
Trump and Kim first met last June in Singapore, a summit that was long on historic pageantry but short on any enforceable agreements for North Korea to give up its nuclear arsenal.
Trump called Kim "Little Rocket Man", while the North Korean leader referred to the United States president as a "dotard". "Given President Trump's serious information and experiential deficit. the North Koreans would readily exploit a free-wheeling one-on-one session".
The United States has also expressed hope that North Korea's economy will grow like that of Vietnam after denuclearization, with President Donald Trump saying it has potential to become an "economic powerhouse" and achieve a "bright future".
Trump has appeared to lower U.S. expectations for the summit, saying that he would be happy if Pyongyang's pause in nuclear and missile testing continued.
The turmoil in Washington has escalated concerns that Trump, eager for an agreement, would give Kim too much and get too little in return. I just don't want testing.
On Thursday, the two leaders will hold "a series of back and forth" meetings, the White House said.
The North also wants increased security guarantees, which could come in the form of a declaration of an end to the 1950-53 Korean War - that culminated with an armistice instead of a full peace treaty - or opening liaison offices.
Instead of insisting on denuclearization first before the US considers any concessions, Biegun says, the U.S.is simultaneously pursuing denuclearization, establishing new U.S.