US President Donald Trump touched down in Japan Sunday, kicking off the first leg of a high-stakes Asia tour set to be dominated by soaring tensions with nuclear-armed North Korea.

Air Force One landed under clear blue skies and Trump stepped out with his wife Melania in bright sunshine to greet the crowds.

Speaking to reporters on the plane, he announced he would likely be meeting Russian President Vladimir Putin during the tour, as the international community seeks a solution to the North Korean missile crisis.

"I think it's expected we'll meet with Putin, yeah. We want Putin's help on North Korea, and we'll be meeting with a lot of different leaders," Trump told reporters on Air Force One.

He added that North Korea was a "big problem for our country and for the world, and we want to get it solved" but had kind words for the people in the hermit state.

"I think they're great people. They're industrious. They're warm, much warmer than the world really knows or understands. They're great people. And I hope it all works out for everybody," he said.

Trump's marathon trip comes with the North Korea crisis at fever pitch, with US bombers running sorties over the Korean peninsula and fears mounting of another Pyongyang missile test.

The president's first stops are Japan and South Korea -- frontline US allies in the effort to force Pyongyang to abandon its nuclear programme, and the two countries with most to fear should a full-scale conflict break out.

Trump and his "friend" Shinzo Abe, Japan's prime minister, enjoy a close personal relationship and the three-day Japan leg of the trip is noticeably relaxed, with the two leaders teeing off for a round of golf before being serenaded by wacky internet sensation Pikotaro.

The Japanese leader has emerged strengthened from a crushing victory in a snap election and has firmly supported Trump in his policy of exerting maximum pressure on Kim, backed up with the threat of military force.

Japan has seen missiles fired over its northern island amid threats by Pyongyang to "sink" it into the sea.

On Saturday, North Korea welcomed Trump to the region with a threat to increase its nuclear arsenal and said the idea of talks was "daydreaming", according to the state-run KCNA news agency.

"Trump only has to play golf in Japan, as he knows Japan will follow (the US) whatever happens. Everything has been sorted out beforehand," Tetsuro Kato, political scientist at Tokyo's Hitotsubashi University, told AFP.

Before the trip, Trump warned China that Japan could take matters into its own hands.

"Japan is a warrior nation, and I tell China and I tell everyone else that listens, I mean, you're gonna have yourself a big problem with Japan pretty soon if you allow this to continue with North Korea," Trump said on Fox News.

While Trump has been in regular contact with the hawkish Abe during the North Korean missile crisis, he pointedly failed to speak to South Korean President Moon Jae-in for several days after Pyongyang's second intercontinental ballistic missile test in July.

Analysts point to Abe and Moon's contrasting approaches to the crisis as an underlying factor, although both leaders will be hoping to press Trump into reaffirming Washington's steadfast commitment to their defence.

Abe has backed his line that "all options," including military action, are on the table, while the more dovish Moon favours engagement with the North to bring it to the negotiating table.

Trump labelled Moon's approach as "appeasement" on Twitter, a comment that did not go down well in the Blue House.

"The two sides have subtle differences in their positions," said Kim Hyun-Wook, a professor at the Korea National Diplomatic Academy. Trump will not follow the well-trodden path to the De-Militarized Zone dividing the Korean peninsula -- a visit derided in Washington as a bit of a "cliche."

The groundwork for Trump's trip was laid by Defence Secretary Jim Mattis, who warned North Korea of a "massive military response, effective and overwhelming," if Pyongyang resorted to using nuclear weapons.

On Friday, US supersonic B-1B Lancer bombers overflew the Korean peninsula, as Seoul's spy agency reportedly warned the North might be readying another missile test.

From Seoul, Trump and his wife Melania travel to China to meet his counterpart Xi Jinping who, like Abe, has solidified his grip on power, after being handed a second term.

He then travels to an APEC summit in Vietnam before heading to a ASEAN gathering of Southeast Asian leaders.

Some observers were fretting that a gaffe by the famously ad-lib president could send tensions rising on the peninsula.

"It will be a disaster if he speaks off the cuff and without thinking," said professor Koo Kab-Woo from the University of North Korean Studies in Seoul.

"If Trump says anything that can provoke North Korea, it could send military tensions soaring again."