US President Donald Trump opened a state visit to Japan by needling the country over its trade imbalance with the United States.

Key points: Mr Trump told business leaders in Tokyo that Japan had had "a substantial edge" in trade with the US for many years

Mr Trump told business leaders in Tokyo that Japan had had "a substantial edge" in trade with the US for many years He said the two countries were "hard at work" on trade negotiations

He said the two countries were "hard at work" on trade negotiations Mr Trump will become the first head of state to meet Emperor Naruhito during his four-day visit to Japan

Mr Trump also promoted the US under his leadership, saying "there's never been a better time" to invest or do business in America, and he urged corporate leaders to come.

The US President's first event after arriving in Tokyo was a reception with several dozen Japanese and American business leaders at the US ambassador's residence. He said the two countries "are hard at work" negotiating a trade agreement.

"I would say that Japan has had a substantial edge for many, many years, but that's OK," Mr Trump said, joking that "maybe that's why you like me so much."

His comments underscored the competing dynamics of a state visit designed to show off the long US-Japan alliance and the close friendship between Mr Trump and Japanese Prime Minister Shinzo Abe even as trade tensions run high.

Mr Trump landed from his overnight flight shortly after a magnitude 5.1 earthquake struck just south of Tokyo and rattled the city.

Mr Abe has planned a largely ceremonial, four-day visit to suit Mr Trump's whims and ego. It is part of Mr Abe's charm strategy that some analysts say has spared Japan from the full weight of Mr Trump's trade wrath.

Mr Abe and Mr Trump plan to play golf on Sunday, before Mr Abe gives Mr Trump the chance to present his President's Cup trophy to the winner of a sumo wrestling championship match. The White House said the trophy is nearly 1.5 metres tall and weighs between 27 kilograms and 32kg.

On Monday, Mr Trump will become the first head of state to meet Emperor Naruhito since he ascended to the throne this month.

Mr Trump will become the first head of state to meet Emperor Naruhito. ( Reuters: Kim Kyung-Hoon )

"With all the countries of the world, I'm the guest of honour at the biggest event that they've had in over 200 years," Mr Trump said before the trip.

The President is threatening Japan with potentially devastating US tariffs on foreign automobiles and auto parts.

He has suggested he will go ahead with the trade penalties if US Trade Representative Robert Lighthizer fails to win concessions from Japan and the European Union.

Mr Trump had predicted that a US-Japan trade deal could be finalised during his trip. But that's unlikely given that the two sides are still figuring out the parameters of what they will negotiate.

He nonetheless portrayed the negotiations in a positive light in his remarks to the business group.

"With this deal we hope to address the trade imbalance, remove barriers to United States exports and ensure fairness and reciprocity in our relationship. And we're getting closer," Mr Trump said.

He also urged the business leaders to invest more in the US.

He praised the "very special" US-Japan alliance that he said "has never been stronger, it's never been more powerful, never been closer."

Mr Abe made a strategic decision before Mr Trump was elected in November 2016 to focus on Japan's relationship with the US.

Mr Trump said relations between the US and Japan had never been closer. ( AP: Kyodo News )

Mr Abe rushed to New York two weeks after that election to meet the president-elect at Trump Tower. Last month, Mr Abe and his wife, Akie, celebrated first lady Melania Trump's birthday during a White House dinner.

Mr Abe and Mr Trump are likely to meet for the third time in three months when Mr Trump returns to Japan in late June for a summit of leading rich and developing nations.

Behind the smiles and personal friendship, however, there is deep uneasiness over Mr Trump's threat to impose tariffs on Japanese automobiles and auto parts on national security grounds. Such a move would be more devastating to the Japanese economy than earlier tariffs on steel and aluminium.

Mr Trump recently agreed to a six-month delay, enough time to carry Mr Abe past July's Japanese parliamentary elections.

US says North Korea missile tests a violation of resolutions

Also at issue is the lingering threat of North Korea, which has resumed missile testing and recently fired a series of short-range missiles that US officials, including Mr Trump, have tried to play down despite an agreement by the North to hold off on further testing.

Mr Trump's national security adviser, John Bolton, told reporters before Mr Trump arrived in Japan that the short-range missile tests were a violation of UN Security Council resolutions and that sanctions must stay in place.

Mr Bolton said Mr Trump and Mr Abe would "talk about making sure the integrity of the Security Council resolutions are maintained."

It marked a change in tone from the view expressed by US Secretary of State Mike Pompeo in a recent television interview.

He said "the moratorium was focused, very focused, on intercontinental missile systems, the ones that threaten the United States."

That raised alarm bells in Japan, where short-range missiles pose a serious threat.

Mr Bolton commented a day after North Korea's official media said nuclear negotiations with Washington would not resume unless the US abandoned what the North described as demands for unilateral disarmament.

AP