North Korea has launched what appeared to be its longest-range ballistic missile yet, with experts suggesting it could reach the US state of Alaska.

The missile test was carried out as the United States prepared to mark its independence day on the Fourth (today) of July.

And as expected, the test triggered a Twitter outburst from President Donald Trump who urged China to “end this nonsense once and for all”.

The North has long had ambitions to build a rocket capable of delivering an atomic warhead to the continental United States – something that Trump has vowed “won’t happen”.

It said it would make an “important announcement” later Tuesday, the South’s Yonhap news agency reported.

Analysts, meanwhile, say the isolated, impoverished country has made great progress in its missile capabilities in the years. According to them, the ascension to power of young leader Kim Jong-Un triggered it. He has overseen three nuclear tests and multiple rocket launches.

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

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

But Tuesday’s launch was the latest in a series of provocations that have ratcheted up tensions, and came days after Seoul’s new leader Moon Jae-In and Trump focused on risks from Pyongyang in their first summit.

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.