US President Donald Trump has landed in Singapore, joining North Korean leader Kim Jong Un in the island city-state ahead of a meeting meant to settle a standoff over Pyongyang's nuclear arsenal.

Air Force One touched down at a military air base, travelling from Canada, where Mr Trump had attended a meeting of the G7.

Hours earlier, a jet carrying Mr Kim landed, and after shaking hands with the Singapore foreign minister, Mr Kim sped through the city's streets in a massive limousine, two large North Korean flags fluttering on the bonnet, surrounded by other black vehicles with tinted windows and bound for the luxurious and closely guarded St Regis Hotel.

Mr Kim smiled broadly as he met with Singapore Prime Minister Lee Hsien Loong.

"The entire world is watching the historic summit between (North Korea) and the United States of America, and thanks to your sincere efforts ... we were able to complete the preparations for the historic summit," Mr Kim told Mr Lee through an interpreter.

Mr Trump is set to meet with Mr Lee on Monday.

The US president has said he hopes to win a legacy-making deal with the North to give up their nuclear weapons, though he has recently sought to manage expectations, saying that it may take more than one meeting.

The North, many experts believe, stands on the brink of being able to target the entire US mainland with its nuclear-armed missiles, and while there is deep scepticism that Mr Kim will quickly give up those hard-won nuclear weapons, there is also some hope that diplomacy can replace the animosity between the US and the North.

This will be the first summit of its kind between a leader of North Korea and a sitting US president.

The North has faced crippling diplomatic and economic sanctions as it has advanced development of its nuclear and ballistic missile programmes.

The North Korean autocrat's every move will be followed by 3,000 journalists who have converged on Singapore up until he shakes hands with Mr Trump on Tuesday.

It is a reflection of the intense global curiosity over Mr Kim's sudden turn to diplomacy in recent months after a series of North Korean nuclear and missile tests last year raised serious fears of war.

Part of the interest in Tuesday's summit is simply because Mr Kim has made such limited appearances on the world stage.

He has only publicly left his country three times since taking power after his father's death in late 2011 - twice travelling to China and once across his shared border with the South to the southern part of the Demilitarised Zone in recent summits with the leaders of China and South Korea respectively.

But it is Mr Kim's pursuit of nuclear weapons that gives his meeting with Mr Trump such high stakes.

The meeting was initially meant to rid North Korea of its nuclear weapons, but the talks have been portrayed by Mr Trump in recent days more as a get-to-know-you session.

Mr Trump has also raised the possibility of further summits and an agreement ending the Korean War by replacing the armistice signed in 1953 with a peace treaty.

China and South Korea would have to sign off on any legal treaty.

It is unclear what Mr Trump and Mr Kim might decide on Tuesday.

Pyongyang has said it is willing to deal away its entire nuclear arsenal if the United States provides it with a reliable security assurance and other benefits.

But many say this is highly unlikely, given how hard it has been for Mr Kim to build his programme and that the weapons are seen as the major guarantee to holding on to his unchecked power.

Any nuclear deal will hinge on North Korea's willingness to allow unfettered outside inspections of the country's warheads and nuclear fuel, much of which is probably kept in a vast complex of underground facilities.

Past nuclear deals have crumbled over North Korea's reluctance to open its doors to outsiders.

Another possibility from the summit is a deal to end the Korean War, which North Korea has long demanded, presumably in part to get US troops off the Korean Peninsula and, eventually, pave the way for a North Korean-led unified Korea.

The fighting ended on July 27 1953, but the war technically continues today because instead of a difficult-to-negotiate peace treaty, military officers for the US-led United Nations, North Korea and China signed an armistice that halted the fighting.

The North may see a treaty - and its presumed safety assurances from Washington - as its best way of preserving the Kim family dynasty.

The ensuing recognition as a "normal country" could then allow sanctions relief, and later international aid and investment.

Just meeting with Mr Trump will also give Mr Kim a recognition North Korea has long sought, setting him up as a global player and equal to the US domestically and, internationally, as the leader of a "normal country" worthy of respect.