And while Australia was still reluctant to accuse Beijing of militarising those islands, he told the US Senate early last year "you'd have to believe in flat Earth to believe otherwise".

Admiral Harry Harris, the commander of US forces in the Pacific, may soon be well-placed to give Australia a lesson in his brand of plain-speak. He's tipped to become the next US ambassador to Canberra, a long-awaited appointment that remains vacant seven months into the administration of Donald Trump.

Despite Admiral Harris' penchant for fiery rhetoric, he is said to be a nuanced military diplomat and strategic thinker, though one who has been a strong proponent privately as well as publicly for the US to more firmly challenge China's island-building by sailing naval ships close to the disputed territory in so-called freedom-of-navigation operations.

News of his possible ambassadorship has been widely welcomed at a time when Canberra is nervous about continuing US engagement given there are few Asia experts in the administration and many key roles remain unfilled.

Admiral Harris, 61, has a good relationship with Prime Minister Malcolm Turnbull - the pair have met several times and are said to get along well - and is liked and respected by Australian military and political leaders.

"Admiral Harris is very well known to us," Foreign Minister Julie Bishop told Sky News on Wednesday after the Washington Post first reported the possible appointment.

"Of course we would welcome such an appointment but we haven't had any official confirmation that a decision has been made."

China is expected to react badly. Beijing reportedly tried to have his command terminated early by offering the Trump administration help on North Korea in return - though Beijing has denied this and Washington never acted on it.

Chinese media have at times attacked him for his background - his mother is Japanese and his father a former US sailor stationed in Yokosuka naval base, though he grew up in Tennessee and still speaks with a southern twang.

But experts cautioned against seeing his appointment purely through a China or military lens.

"Given his experience, I have no doubt that Admiral Harris fully appreciates and will be sensitive to Australia's China equities," said Andrew Shearer, who was former prime minister Tony Abbott's national security adviser and is now at the Washington-based Centre for Strategic and International studies.

"If anything, I'd expect him to overcompensate for his background and emphasise the full breadth and depth of Australia's engagement with the United States."

Ashley Townshend of the US Studies Centre at the University of Sydney said Admiral Harris would want to use the position to advance his agenda of strengthening regional co-operation to "check Chinese power and respond to potential or future acts of aggression or coercion".

Bu he added that Admiral Harris has always been respectful in discussing the security role Australia plays in the region. As an Asia expert, he would understand how the alliance needed to evolve in the Asian century, Mr Townshend said.

James Goldrick, a former Navy rear admiral and now military scholar, said Admiral Harris had "strong views and would express them firmly but reasonably".

"He is not like something out of Full Metal Jacket," he said.

Admiral Harris is not especially close to Mr Trump - which might be a concern at a time when direct access to the Oval Office is especially important.

But experts said that his powerful place in the institutions that keep the Australia-US relationship humming along, plus Mr Trump's fondness for military figures, suggests Admiral Harris would have clout.

Mr Townshend said the Pentagon was currently the most effective arm of the US administration and this would work in Admiral Harris' favour.

"Harris has succeeded in advancing his agenda towards more robust and regular freedom-of-navigation operations," he said. "That suggests he has a good relationship with the gatekeepers on the National Security Council around Trump's Asia policy and he's able to work effectively with them," he said.

"Personal access is not Harris' strength. His strength would be his interconnectedness and knowledge he has of every level of the Australia-US relationship."