AUSTRALIA will join military action against North Korea if the rogue nation fires a nuclear warhead at the United States, acting Prime Minister Barnaby Joyce has confirmed.

As Malcolm Turnbull heads to Germany for talks with other G20 leaders, Mr Joyce is ramping up pressure on China to step in and “stop this madness”. His call comes after US ambassador to the United Nations Nikki Haley warned that America would use force “if we must” against North Korea, after Pyongyang tested an intercontinental ballistic missile with the potential to reach Darwin or Alaska.

“No one should ever go too far in testing the resolve of the United States of America,” Mr Joyce told Sky News on Thursday.

“If North Korea was to deliver a warhead into the United States of America then the ANZUS alliance would be called in.” Asked what action that may involve, Mr Joyce said: “What would you want?” “If someone drops a nuclear warhead on a country what do you think happens next?” One of Australian’s most senior military commanders insists the risk of a strike on the country’s north by North Korea remains low.

Chief of Joint Operations Vice Admiral David Johnston said that despite Pyongyang’s aggressive demonstrations, the range and capability of the missile launched this week is still to be determined.

“There is very little risk at the moment to the northern part of our country,” he told reporters in Canberra.

“But it’s an area where North Koreans have clearly demonstrated capability and we all need to better understand it — including what the consequences may be from a military perspective.” Given the low threat to Australia’s mainland, Vice Admiral Johnston said there hasn’t been an immediate focus on amassing a system to defend against missiles. The focus now was on applying diplomatic pressure on North Korea to stop their nuclear program and the development of missile technology.

“Where there’s emerging issues that require military support, the ADF has the capability to provide the government (with) options and we’re able to do so.” Earlier, Mr Joyce revealed Australia had “sympathy” with calls to impose trade sanctions on countries such as China, in retaliation for giving North Korea an economic lifeline.

Mr Joyce argued the greatest economic threat to China was North Korea’s potential to create instability in the region.

Asked about a US warning to cut off trade with countries doing business with North Korea, he told ABC radio: “We obviously have sympathy.” But Mr Joyce warned the effect of trade sanctions would pale into insignificance against what would happen if North Korea continues down its nuclear program path.

“If North Korea was to make a mistake in one of its launches ... and drop one of their missiles into South Korea or onto Japan then the economic plan for China, the economic plan for South East Asia would cease that moment.” Labor called on the prime minister and foreign minister to clarify whether the government was considering such sanctions.

“The government must urgently clarify this, and one day into his overseas travel, the prime minister must pull his deputy into line,” opposition trade spokesman Jason Clare and foreign affairs spokeswoman Penny Wong said. Trade sanctions on China would devastate Australian farmers, they said.