SEOUL, North Korea launched a ballistic missile Tuesday as the US prepared to mark its Independence Day, triggering a Twitter outburst from President Donald Trump who urged China to "end this nonsense once and for all".

The launch was the latest in a series of provocations that have ratcheted up tensions over the nuclear-armed North's weapons ambitions, and came days after Seoul's new leader Moon Jae-In and Trump focused on the Pyongyang threat in their first summit.

The "unidentified ballistic missile" was fired from a site in North Phyongan province, the South's Joint Chiefs of Staff said in a statement, and came down in the East Sea, the Korean name for the Sea of Japan.

It flew for "more than 930 kilometres", they added.

The device may have come down in Japan's exclusive economic zone, a spokeswoman for Tokyo's defence ministry told AFP -- waters extending 200 nautical miles from its coast.

Japanese Chief Cabinet Secretary Yoshihide Suga said the missile flew "for about 40 minutes" -- an unusually long flight time, with Prime Minister Shinzo Abe telling reporters: "This launch clearly shows that the threat has grown."

The US, Japan and South Korea will hold a summit on the sidelines of this week's G20 meeting on the issue, he added. "Also I will encourage President Xi Jinping and President Putin to take more constructive measures."

The United Nations has imposed multiple sets of sanctions on Pyongyang over its weapons programmes, which retorts that it needs nuclear arms to defend itself against the threat of invasion.

It has a goal of developing a missile capable of delivering a warhead to the US mainland -- something that Trump has vowed "won't happen".

There are doubts whether the North can miniaturise a nuclear weapon sufficiently to fit it onto a missile nose cone, or master the technology needed for it to survive re-entry into the Earth's atmosphere.

But analysts say the isolated, impoverished country has made great progress in its military capabilities in the years since young leader Kim Jong-Un inherited power.

In response to the latest launch, Trump asked on Twitter: "Does this guy have anything better to do with his life?"

US Pacific Command confirmed the test and said it was a land-based, intermediate range missile that flew for 37 minutes and did not pose a threat to North America.

But David Wright, of the Union of Concerned Scientists, said the available figures implied a significant increase in the range of Pyongyang's missiles.

The missile would have had to have flown on a "very highly lofted trajectory" and reached a maximum altitude of more than 2,800 kilometres, he said.

"If the reports are correct, that same missile could reach a maximum range of roughly 6,700 km on a standard trajectory," he wrote on the organisation's allthingsnuclear blog.

"That range would not be enough to reach the lower 48 states or the large islands of Hawaii, but would allow it to reach all of Alaska."

-AFP