Tuesday's meeting will be the first between a sitting US president and a leader of North Korea, whose nuclear and ballistic missile ambitions have raised global concerns and seen tensions soar.

It is an extraordinary turnaround from the rhetoric of last year, when Trump threatened the North with "fire and fury" and Kim dubbed him a "mentally deranged US dotard".

The summit has raised hopes of progress towards a peace treaty to formally end the Korean War, the last festering legacy of the Cold War, after hostilities only stopped with an armistice.

But Pyongyang is demanding as yet unspecified security guarantees and the end of what it calls a "hostile policy" towards it, and has not made clear what concessions it is offering over the nuclear arsenal it calls its "treasured sword" to defend against a US invasion.

The North, which has been subjected to increasingly strict sanctions by the UN Security Council and others, has made promises of change in the past, such as at the lengthy Six Party Talks process, only for the agreements to collapse later.

"We remain committed to the complete, verifiable, irreversible denuclearisation of the Korean Peninsula," Secretary of State Mike Pompeo tweeted.

The mercurial US leader has whipsawed on expectations for the meeting, signalling that it could be the beginning of a "process" of several meetings, only to call it a "one-time shot" for peace as he embarked for Singapore.

He would know "within the first minute" whether an agreement would be possible, he added.

"Great to be in Singapore, excitement in the air!" he tweeted Monday.

The North has sought such a meeting for decades, where its leader will meet a US president as an equal rather than as the representative of a pariah state.

But analysts warn that it risks being more of a media event than an occasion of substantial progress and delegations from the two sides were negotiating at a neutral hotel in Singapore to try to address their differences.

The previous US stance, said Bruce Klingner of the Heritage Foundation, was that "we don't deploy a president to negotiate a treaty, we deploy a president to sign a treaty where we know where every piece of punctuation is on that piece of paper".

"One of my worries is that we come out of this Singapore summit with something that looks remarkably like the Six Party Talks or anything that the president has previously criticised but it is hyped as something that's historic and new and groundbreaking," he added.

- Separate planes -

Heavy security and armed police were in place at summit-related venues across the city-state.

Outside the Istana, the presidential palace where Trump was due to meet Singaporean Prime Minister Lee Hsien Loong, well-wishers displayed American flags and a boy held up a sign reading: "I love President Trump!"

The North's official KCNA news agency called the summit "historic", saying it would take place in a "changed era" and "under the great attention and expectation of the whole world".

Kim would exchange "wide-ranging and profound views" on issues including "building a permanent and durable peace-keeping mechanism on the Korean peninsula" and "realising the denuclearisation of the Korean peninsula", it added.

It formally referred to Trump by his full name in the Monday report, including his middle initial -- the first time it has done so.

The Rodong Sinmun newspaper, the mouthpiece of the ruling Workers' Party, devoted its first two pages and 16 photos to Kim's trip, including images of him boarding an Air China Boeing 747 for the journey.

His sister and close aide Kim Yo Jong is also in Singapore, and is believed to have travelled separately on the ageing Soviet-made Ilyushin-62 that is Kim's personal aircraft.

US presidents and vice-presidents generally never fly on the same aircraft to guarantee that one of them survives in the event of a disaster, and the move appeared designed to ensure the preservation of the Kim dynasty, which has ruled the North for three generations.

Under Kim, Pyongyang has made rapid progress in its weapons technology, carrying out by far its most powerful nuclear test to date last year and launching missiles capable of reaching the US mainland.

But the South's Winter Olympics in February were the catalyst for a flurry of diplomatic moves as South Korea's dovish leader Moon Jae-in sought to bring the two sides together, holding two summits of his own with Kim in the Demilitarized Zone that divides Korea.