US President Donald Trump has arrived in Singapore ahead of a potentially historic summit with North Korean leader Kim Jong Un, the first meeting between the leaders of two countries that have been sworn enemies for almost seven decades.

He arrives after throwing the Group of Seven meeting of the world's leading industrialised nations into chaos with a withering tirade over trade agreements.

Just as the Canada-hosted G-7 meeting had seemed to weather Trump's threats of a trade war, the US president backed out of the group's joint statement that Canadian PM Justin Trudeau said all the leaders had come together to sign.

EVAN VUCCI/AP

Trump and Kim are both in Singapore, awaiting their Tuesday summit.

Trump called Trudeau "dishonest & weak" after Trudeau said Canada would retaliate for new US tariffs.

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Later, the White House levelled more unprecedented criticism against Canada's prime minister, branding Justin Trudeau a back-stabber unworthy of Trump's time.

TERENCE TAN/AP

North Korean leader Kim Jong Un arrived in Singapore earlier on Sunday and was met by government officials.

"There's a special place in hell for any foreign leader that engages in bad faith diplomacy with President Donald J. Trump and then tries to stab him in the back on the way out the door," Trump trade adviser Peter Navarro said in an interview nationally broadcast in the United States.

Canada's foreign minister, Chrystia Freeland, said her country "does not conduct its diplomacy through ad hominem attacks."

The verbal volleys by Navarro and Trump's top economic adviser, Larry Kudlow, picked up where Trump left off on Saturday evening with a series of tweets from Air Force One en route to the Kim summit. Kudlow suggested Trump saw Trudeau as trying to weaken his hand before that meeting, saying the president won't "let a Canadian prime minister push him around. ... Kim must not see American weakness".

Trump arrived in Singapore after meeting with other world leaders at the G7 summit.

TRUMP TOUCHES DOWN

Air Force One touched down with little fanfare at Paya Lebar Air Base in Singapore, landing a few hours after Kim arrived in the island state.

Trump waved as he stepped off the presidential jet, briefly greeted Singaporean officials on the tarmac and quickly climbed into a limousine to head to his hotel for the evening.

Asked upon his arrival how he was feeling about the summit, Trump told reporters, "Very good".

Trump and Kim are scheduled to meet face-to-face on Tuesday, and it remains far from clear what kind of agreement on North Korea's nuclear programme the two leaders will be able to forge.

Trump was upbeat as he departed Canada on Saturday for his day-long journey halfway around the globe, which included a refuelling stop on the Greek island of Crete.

The president told reporters he would rely on his intuition to size up Kim's intentions regarding a deal to abandon his nuclear arsenal.

"Within the first minute, I'll know," he said. "My touch, my feel - that's what I do."

Kim and Trump are to meet at the Capella hotel on the resort island of Sentosa, usually better known for hosting Singapore's Universal Studios amusement park.

Singapore's prime minister, Lee Hsien Loong, welcomed Kim and his entourage to the Istana, his palatial office, for talks laying the groundwork for Tuesday's summit. Trump is due to meet with Lee on Monday.

"From our point of view, it's important that the meeting take place and that the meeting sets developments on a new trajectory - one that will be conducive to the security and stability of the region," Lee told reporters here earlier in the afternoon.

Also on Monday, Sung Kim, the US ambassador to the Philippines who has helped lead pre-summit negotiations with North Korea, will lead an administration working group with a North Korean delegation at the Ritz Carlton, press secretary Sarah Huckabee Sanders said in a statement late on Sunday.

Video broadcast by the prime minister's office showed Kim and Lee shaking hands and posing for photos at the Istana on Sunday evening. Kim could then be seen introducing Lee to his senior officials, while his sister and close aide, Kim Yo Jong, could be seen in the background.

TRYING TO CATCH A GLIMPSE OF KIM

The North Korean leader landed at Singapore's Changi airport and travelled in his armoured Mercedes-Benz limousine through one of the island state's swankiest shopping districts to the five-star St Regis Hotel.

The streets were lined with tourists and journalists trying to catch a glimpse of the enigmatic North Korean leader, who has embarked on his farthest journey - and the journey with the highest stakes - since taking power at the end of 2011.

Kim has engaged in a flurry of diplomacy this year, holding two meetings with South Korean President Moon Jae-in and two with China's Xi Jinping, leading to this first-ever summit between a North Korean leader and a sitting US president.

After overseeing rapid advances in North Korea's nuclear and missile technology last year, Kim now appears to be turning his attention to his country's economy and particularly to getting rid of the international sanctions that are hampering its growth.

The nuclear programme has enabled Kim to project confidence, analysts say, and he is now trying to metamorphose from a nuclear-armed tyrant into a responsible international statesman.

Kim's 5000-kilometre journey from North Korea was full of intrigue, with three planes departing from Pyongyang on Sunday morning.

The first was a cargo plane believed to be carrying vehicles and supplies for the North Korean leader.

The second was an Air China Boeing 747, usually used by the Chinese government to carry high-level officials, that took off at 8.30am, about an hour after it arrived from Beijing.

Then Kim's private jet, a Soviet-made Ilyushin-62, officially called "Chammae-1" after North Korea's national bird but sometimes jokingly referred to as "Air Force Un," departed at about 10am local time.

Kim had taken this third plane when he travelLed to the Chinese city of Dalian in May to meet President Xi Jinping, a trip that was viewed as a practice run for the Singapore journey.

But Kim was in fact on the Air China plane. Kim Yo Jong arrived in Singapore on the North Korean jet about an hour after her brother.

Commentators in South Korea speculated that this was part of an effort to create a decoy so that no one - not even the Chinese - knew which plane the North Korean leader was traveLling on.

Kim was greeted at Changi Airport by Singapore's foreign minister, Vivian Balakrishnan, who had just returned from a five-day trip to Washington and Pyongyang.

The North Korean leader was accompanied by officials including Kim Yong Chol, a top aide who delivered a letter to Trump in the White House earlier this month; Ri Su Yong, who is in charge of international relations in the ruling communist Workers' Party and was ambassador to Switzerland while Kim Jong Un was at school there; and foreign minister Ri Yong Ho.

Television footage showed they travelled from the airport in a large convoy of vehicles with a heavy police guard.

Kim Jong Un appeared to be in a black Mercedes-Benz stretch limousine like the one he used for the inter-Korean summit in April. Although he was not visible through the black tinted windows, the car was flying a North Korean flag and the ensign of North Korea's State Affairs Commission, of which Kim is the chairman.

The leader went straight to the St Regis Hotel, a place that his older half brother, Kim Jong Nam, was known to frequent. Kim Jong Nam, who lived in Macau, was killed in a chemical weapon attack in Kuala Lumpur airport last year - an assassination widely believed to have been ordered by Kim Jong Un to eliminate a potential rival for power.

The 334-square-metre presidential suite at the St. Regis goes for about NZ$11,373 a night. It has its own private gym and Jacuzzi, a baby grand piano, custom-made Czech crystal chandeliers and art works including a Marc Chagall painting.

It is not clear who is picking up the tab for Kim Jong Un's stay.

- Washington Post, AP