Trump tees up Japan summit with Abe golf match

US President Donald Trump teed off Sunday with "golf buddy" Japanese Prime Minister Shinzo Abe as the pair relaxed before official talks likely to touch on trade and North Korea.

On a sweltering cloudless Tokyo morning, where the temperature was expected to climb above 30 degrees Celsius (86 Fahrenheit), Trump's Marine One helicopter thundered down, briefly breaking the serenity of the Mobara course in Chiba, outside the capital.

Abe, wearing white trousers and blue sport coat was there to meet Trump, then took the wheel of the golf cart for his guest, who was dressed in a red sweater and black trousers with a red USA cap.

Following breakfast at the club, the two golfers were reportedly due to play 16 holes, the other two holes taken up by helicopters and security.

An excited Trump tweeted: "Going to play golf right now with @AbeShinzo. Japan loves the game."

Earlier Sunday, Trump had taken to Twitter in an apparent bid to ease mounting tensions with North Korea, which has conducted two missile tests after a February summit in Hanoi collapsed without agreement.

Dismissing the missiles as "some small weapons", he said the tests had "disturbed some of my people, and others, but not me".

One of his "people", National Security Advisor John Bolton, had said the previous day that there was "no doubt" the launches had contravened UN Security Council resolutions.

But Trump said: "I have confidence that Chairman Kim will keep his promise to me."

The American president maintains that the North Korean leader had pledged he was serious about denuclearisation but experts say there is still a wide gulf between the two sides over what that means exactly.

Abe is arguably Trump's closest foreign ally and the pair have cemented their diplomatic bromance over a shared love of golf, which they play whenever possible.

The Japanese PM once presented Trump with a gold-plated club worth $3,755 and has been getting some practice in before teeing off on Sunday.

Trump's Secret Service detail will doubtless be hoping there is no repeat of the 5.1-magnitude earthquake that rocked Tokyo just over an hour before Trump arrived on Saturday, with the epicentre very close to the golf club.

After the golf, the two leaders will take in the final day of the sumo "basho" or tournament. Trump will present Japanese grappler Asanoyama with the "President's Cup" -- weighing 60-70 pounds (27-32 kilograms) and measuring 54 inches (1.4 metres).

On Monday, the serious diplomacy begins, with Trump set to be the first foreign leader to meet Japan's new emperor, Naruhito, who ascended the Chrysanthemum Throne at the beginning of the month after his father's abdication, the first in more than 200 years.

The United States and Japan, respectively the world's top and third-biggest economies, are also in the process of negotiating a delicate trade deal.

Trump wasted little time upon arrival in attacking what he sees as an imbalanced trade relationship, vowing it would become "a little bit more fair" after a deal was inked.

However, experts believe that with Abe facing upper house elections expected in July -- with persistent rumours he will also call a snap general election -- little concrete progress will be made on this front.

Trump's top trade representative Robert Lighthizer spent more than two hours locked in talks with his Japanese counterpart, Economy Minister Toshimitsu Motegi, Saturday night but there was no sign of a breakthrough.

"Our understanding on our positions and the way we think further deepened" after the meeting, Motegi told reporters.

"But it doesn't mean our positions are in perfect harmony. We agreed to make efforts to fill in the gap," he said, without giving more precise details.

"We agreed to make efforts to strike the deal soon... but I don't think we'll sign the agreement on the 27th (of May)."