Kim Jong-un arrives in Vietnam for second summit with Donald Trump

North Korea's Kim Jong-un arrived in Vietnam on Tuesday in his heavily armoured train, a day ahead of his two-day summit with US President Donald Trump where the two leaders were expected to build upon their agreement to "work toward complete denuclearization of the Korean Peninsula".

After traveling for over 60 hours by train all the way from Pyongyang through China, Kim arrived on Tuesday morning to a red carpet welcome at 8.15 a.m., at the station in Dong Dang town, some 136 km from Hanoi, CNN reported.

At the station, Kim, dressed in a black Mao-style suit, waved and smiled as he was greeted by Vietnamese officials and a guard of honour before getting into his Mercedes and setting off for Hanoi where he will hold the summit with Trump on Wednesday and Thursday.

Trump is due to land at the Noi Bai International Airport in the Vietnamese capital on Tuesday night.

"Heading over to Vietnam for my meeting with Kim Jong Un. Looking forward to a very productive Summit," he tweeted on Monday night aboard the Air Force One.

The two leaders will begin the summit with a one-on-one meeting and a social dinner, to be joined by their top aides, in Hanoi on Wednesday night. Secretary of State Mike Pompeo is already in Hanoi, reports Yonhap News Agency.

Kim and Trump will have follow-up talks on Thursday in a bid to flesh out the details of their Singapore accord that was signed during their first historic meet last June, in which they agreed to work together for "complete denuclearization", transformation of Pyongyang-Washington relations and a peace regime.

The summit location in Hanoi remains unannounced amid speculation that the Sofitel Legend Metropole hotel right next to the government guesthouse, where North Korea's advance team is staying, has been chosen.

Kim is expected to stay at the Melia Hanoi Hotel.

According to sources, a major focus of the summit will be whether the two leaders can produce a joint declaration calling for concrete steps toward denuclearization by North Korea and corresponding US measures that satisfy Pyongyang.

Kim is expected to call on the US to let its guard down and relax sanctions on Pyongyang.

The format in which they could announce their agreement, if they reach one, is also grabbing attention. Observers do not rule out the possibility of a joint press conference, a routine post-summit ceremony for Trump and other foreign leaders.