Security and defense officials on Guam say there is no imminent threat to people there or in the Northern Mariana Islands after North Korea said it was examining its operational plans for attack.
The 1951 Australia, New Zealand and United States Security Treaty compels the three parties to respond to an armed attack on any of them.
Mr Trump has warned he would not allow Pyongyang to develop nuclear weapons capable of hitting the US.
"Australia would come to the aid of the U.S.as America would come to our aid if we were attacked", Turnbull said, according to the Australian Broadcasting Corporation.
The article goes on to say that the plan will be reported to the Supreme Command, and await Kin Jong Un's decision.
The prime minister discussed the unfolding situation with US Vice President Mike Pence on Thursday night and received a briefing from the Chief of the Defence Force Mark Binskin in Canberra on Friday.
The manner of action depends on the circumstances, Turnbull added.
He remains focused on peaceful resolution, working with the UN, US, China and Russia to put pressure on North Korea.
This recalls unfortunate prime ministerial contributions such as Harold Holt's "all the way with LBJ" at the time of Vietnam, or John Howard's characterisation of Australia as America's "deputy sheriff" in the Asia-Pacific.
Rhetoric has escalated on both sides, with US President Donald Trump threatening swift retaliation. "That's the preferred way to deal with it", he said.
Greens leader Richard Di Natale said Mr Trump was "unhinged and paranoid" and Australia should distance itself from the US alliance.
He wrote in The Strategist: "At the signing of the armistice in Korea in 1953 we agreed, with South Korea's allies, that we would defend the South in the event of an attack by the North". Australia's support for the US in Afghanistan was part of a NATO deployment.
The former Labor PM Kevin Rudd told Fairfax Australia would be "well advised to begin analysing ballistic missile defence needs, available technologies and possible deployment feasibility for northern Australia".
It is not clear that North Korea has achieved this level of sophistication.
This presidency is unlike any of its modern predecessors, and judging how to handle it is extremely difficult for the government.
The prime minister said of North Korea's regime: "Its conduct is illegal, it's reckless, it's provocative, it's dangerous". It's interesting to note the new administration hasn't yet even posted an ambassador to Australia. They also reflect, unvarnished, the reality that Australia always answers America's call.
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