"If there's an attack on the US, the ANZUS (Australia, New Zealand, US Security) Treaty would be invoked and Australia would come to the aid of the US, as America would come to our aid if we were attacked." Turnbull said.
Turnbull added that in the event of an attack, "how that manifests itself obviously will depend on the circumstances and the consultations with our allies", reports Efe news.
The Prime Minister has already discussed the issue in a telephone conversation with US Vice President Mike Pence, whom he assured that Australia's commitment to support the US is "rock-solid".
In 1951, Australia, New Zealand and the US signed the ANZUS Security Treaty Alliance, which was last invoked by the Australian government following the September 2001 terror attacks in the US.
On Tuesday, North Korea announced that it was preparing to fire four mid-range missiles in mid-August towards waters near Guam, an American territory located in the Western Pacific where strategic US Navy and Air Force bases are stationed.
Trump previously responded to the threat saying that the US is ready to respond to North Korean attacks on Guam "with fire and fury like the world has never seen", and also announced an increase in the spending on anti-missile systems amid escalating tensions with Pyongyang.
According to the US intelligence service, North Korea could already have a nuclear warhead small enough to mount on an intercontinental missile.
Turnbull's confirmation came just a day after Foreign Minister Julie Bishop refused to speculate as to whether Australia would invoke ANZUS in the event of conflict, reports Xinhua news agency.
She told the Australian Broadcasting Corporation (ABC) that Australia was "not a party, in the legal sense, to the (current) Korean War armistice", and was at the time hesitant to declare its support for the US.
"As far as the ANZUS security alliance is concerned, that is an obligation to consult," Bishop said on Thursday morning
Meanwhile, Australia's opposition Labor party has declared that it would work with the government in a bipartisan approach to the escalating tensions between Pyongyang and Washington.
"Australians should be reassured that on this matter ... the politics of Labor and Liberal are working absolutely together," Labor leader Bill Shorten told the media here on Friday.