Scott Morrison has drawn a "red line" in the Pacific, declaring that China will not build a military base "on our doorstep".
As the prime minister faces ongoing questions about his government's handling of relations with Pacific Island neighbours in the wake of China's security pact with the Solomon Islands, Mr Morrison sought to assure critics his government has not ceded the balance of power in the region.
Speaking on Sunday, Mr Morrison made the vague declaration, suggesting a military installation would trigger action from Australia and the United States.
"This is a shared concern, not just Australia, this is Australia and regional governments, particularly places like Fiji and Papua New Guinea." he said.
"Working together with our partners in New Zealand and of course the United States, I share the same red line that the United States has when it comes to these issues.
"We won't be having Chinese military naval bases in our region, on our doorstep."
When pressed on what such a "red line" meant in practice, Mr Morrison would not articulate.
When asked how he would stop a base from materialising, he also avoided the question.
"Well, what would you do to stop [it]? A blockade?" a journalist asked.
"Well, let me first be clear, that Prime Minister Sogavare has been very clear to me, saying there will be no such bases. So that is what he has said. And so he clearly shares our red line," Mr Morrison responded.
It comes after the White House issued a statement saying such a move by China would see the US "respond accordingly". The statement was issued in the wake of a high-level US delegation being sent to the Solomon Islands.
"If steps are taken to establish a de facto permanent military presence, power-projection capabilities, or a military installation, the delegation noted that the United States would then have significant concerns and respond accordingly," it said.
A Chinese naval base in the Solomon Islands could see shipping routes from Australia to Asia cut off during a conflict.
"If China established a military base in the Solomon Islands, that is going to represent a threat to the east coast that we haven’t seen since the Second World War," Peter Jennings, executive director of the Australian Strategic Policy Institute, told Radio National on Monday.
He said Australia's soft power operations in the Pacific have been "operated on the smell of an oily rag".
"It’s going to cost more than that ... We need to be less inclined to ride on the coattails of the United States and be prepared to front up and pay for the cost of our own security," he said.
Mr Morrison has faced sustained criticism of the Solomon Islands deal happening on his watch, with Labor's Shadow Foreign Affairs spokesperson Penny Wong saying if Labor was elected in May it would increase foreign aid to the Pacific to secure the region.
She also pointed to recent comments to accuse Mr Morrison of always trying to take credit without actually doing the job. As recently as March, the PM said: "I talk to Pacific leaders every single week and that is what ensures that we can block the incursion into our region."
What does the 'red line' threat actually mean?
The prime minister on Sunday would not say what his government would do to respond to a Chinese military base if he remained in office.
Shadow Defence Minister Brendan O'Connor on Monday said Labor will seek a briefing to better appreciate the government's stance but said the "red line" threat was "too little, too late".
"Given the change in tone and rhetoric and words used by the prime minister, we will seek a briefing from the government," he told the ABC.
Nonetheless he said Labor "understands" what is meant by the claim – an apparent suggestion it would prompt a diplomatic or even military response.
"Yes we understand what the prime minister means by that," he said, but he derided Mr Morrison for "post-facto rhetoric".
"We needed to see better investment and better engagement in the region ... rather than react after the fact."
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