The escalation in the war of words comes after President Donald Trump tweeted Kim Jong Un "won't be around much longer."
Australia must develop greater missile defences against a strike from North Korea.
That's the advice from Dr Brad Roberts, who served as US deputy assistant secretary of defence for nuclear and missile defence policy between 2009 and 2013.
Roberts, who is in Australia briefing officials about regional threats, told theABC it doesn't have to be too costly.
"I don't think it's a large number of very expensive interceptors and radars deployed around the periphery of the Australian continent," he said. "A sea-based capability on the advanced destroyer that would include a sea-based radar and some interceptors: that could operate in coalition partnership with other allies."
North Korean leader Kim Jong-un wants to make us fearful, Dr Brad Roberts says. Photo / AP
Roberts said Australia could be hit by a North Korean missile.
"Unfortunately, Australia doesn't really get to choose whether or not North Korea threatens it - it's the choice that the North Korean leader [Kim Jong-Un] makes," he said.
"His objective is to make us fearful so that our leaders will not stand up to his threats and coercion."
Minister for Defence Industry Christopher Pyne. Photo / AAP
Defence Industry Minister Christopher Pyne said last month that the Government was considering upgrading the Navy's new air warfare destroyers to include missile defence shields.
"In the Defence White Paper, and the integrated investment plan, upgrades of the warfare destroyer capabilities have been already flagged," Pyne said.
China orders North Korea businesses closed
It came as China ordered North Korean-owned businesses to close, cutting foreign revenue for the isolated country under UN sanctions imposed over its nuclear and missile programmes.
China is North Korea's main trading partner, making Beijing's cooperation essential to the success of sanctions imposed in an effort to top the North's pursuit of weapons technology. China has long been North Korea's diplomatic protector but has gone along with the latest penalties out of growing frustration with Kim Jong-Un's government.
North Korean businesses and ventures with Chinese partners must close within 120 days of the September 11 approval of the latest sanctions, according to the Ministry of Commerce. That would be early January.
China's President Xi Jinping. Photo / AP
North Korean companies operate restaurants, trading outfits and other ventures in China, helping to provide the north with foreign currency.
The latest round of sanctions approved by the UN Security Council ban member countries from operating joint ventures with North Korea.
The sanctions also ban sales of natural gas to North Korea and purchases of the North's textile exports, another key revenue source.
They order other nations to limit fuel supplies to the North.
China, which provides the bulk of North Korea's energy supplies, announced Saturday it would cut off gas and limit shipments of refined petroleum products, effective from January 1.
United States Ambassador to the United Nations Nikki Haley speaks after voting to adopt a new sanctions resolution against North Korea during a meeting of the UN Security Council. Photo / Ap
It made no mention of crude, which makes up the bulk of Chinese energy supplies to North Korea and is not covered by the UN sanctions.
China also has banned imports of North Korean coal, iron and lead ore, and seafood since early September.
On Thursday, the Ministry of Commerce defended its recent imports of North Korean coal as permitted by UN sanctions.
A ministry spokesman, Gao Feng, said imports that were reported in August trade data were allowed by a "grace period" for goods that arrived before the UN ban took effect. The imports are "in line with the [UN] resolution", Gao said.
