'In three years': N Korea making missiles which 'could hit Australia'

North Korea could potentially hit Australia with one of its under-development intercontinental ballistic missiles (ICBM) within the next three years, according to military experts.

With tensions continuing to boil between the United States and the Democratic People's Republic of Korea (DPRK), Australia's Prime Minister Malcolm Turnbull has joined President Donald Trump in leaning on China to step up and defuse matters.

Australia and New Zealand stiffened their rhetoric against North Korea Sunday after the isolated state threatened Canberra with a nuclear strike, urging it to think twice before "blindly and zealously toeing the US line".

The move comes as US Vice President Mike Pence wraps up an Asia tour, which has included visits to South Korea, Japan and Australia partly to reassure allies amid fears that Pyongyang may be readying for a sixth nuclear test.

"If Australia persists in following the US' moves to isolate and stifle North Korea... this will be a suicidal act," a North Korean foreign ministry spokesman said after Australian Foreign Minister Julie Bishop called the hermit state a "serious threat".

The spokesman, speaking to the North's official KCNA news agency, warned Bishop to "think twice about the consequences".

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Ms Bishop added on Sunday that the North Korean government "should invest in the welfare of its long-suffering citizens, rather than weapons of mass destruction".

Lowy Institute director of International Security Euan Graham told Fairfax Media that while North Korea had not yet developed a nuclear ICMB that is capable of striking Australia, it appeared on track to do so.

"They probably will within the life of the Trump administration," he said.

"The system they are developing would allow them to hit anywhere in the continental United States."

Mr Euan said that at present China and Russia had the nuclear capability of striking the mainlined US, but expanding that club is something "any US administration would try to prevent from happening".

Director of the Australian Strategic Policy Institute, Peter Jennings, told Fairfax North Korea "doesn't have the ability yet to hit us with a missile that carries a nuke", as it edges closer to nuclear ICMB capability a pre-emptive strike will look more attractive to the US.

"That's some years away, if they ever get there," Mr Jennings said, suggesting a likely target would be the Pine Gap joint US-Australia military intelligence base near Alice Springs.

A more present and likely threat Australia should be concerned about is "some kind of cyber attack", Mr Jennings said, which the DPRK "are quite good at" and carry out regularly on South Korea.

Australia's neighbour and long-time ally New Zealand has since accused North Korea of having "evil intent".

Defence Minister Gerry Brownlee told Television New Zealand on Sunday people knew little about Kim Jong-Un's regime but "you would assume that underneath him there is a very big machinery of people who have equally evil intent".

"It's North Korea that is sending the missiles into the Sea of Japan and making the various outrageous threats including the threats overnight to Australia," he added.

The reclusive state has long been seeking to develop a long-range missile capable of hitting the US mainland with a nuclear warhead, and has so far staged five atomic tests, two of them last year.

Mr Pence vowed Wednesday that the US would counter any attack with an "overwhelming and effective" response after a senior North Korean official pledged weekly missile tests and "all-out war" if the US took any action against it.

In Sydney, the VP maintained calls for Pyongyang's sole ally China to do more to rein in its neighbour.

Mr Turnbull also urged China to use its leverage over the hermit state, describing the North Korean regime as "reckless and dangerous".

He added that Australia and the US were "absolutely united" in their determination to achieve a nuclear-free Korean peninsula.

Supercarrier Carl Vinson is due to start joint exercises with Japan's navy on Sunday, Tokyo's defence ministry said, with the drills expected to last several days and involve two Japanese warships.

- With AFP