(CNN) In a remarkably blunt speech, US Sen. John McCain has called China a "bully" who is using its new found strength to remake the world order to better favor its needs.

"The challenge is that as China has grown wealthier and stronger, it seems to be acting more and more like a bully," the Republican senator from Arizona and 2008 presidential candidate said during a speech as a guest of the US Studies Center at the University of Sydney

"It is refusing to open more of its economy so that foreign businesses can compete fairly. It is stealing other peoples' intellectual property. It is asserting vast territorial claims that have no basis in international law. And it is using its trade and investment as tools to coerce its neighbors," McCain added.

To an audience which included former Australian Prime Ministers John Howard and Bob Hawke, McCain also criticized the Trump administration for not doing enough to preserve the current geopolitical status quo.

"I realize that I come to Australia at a time when many are questioning whether America is still committed to these values. And you are not alone. Other American allies have similar doubts these days. And this is understandable. I realize that some of President Trump's actions and statements have unsettled America's friends," the Republican senator from Arizona and 2008 presidential candidate said

Though McCain has been outspoken about his belief that the Trump administration should take a more globalist approach to US foreign policy, such unvarnished criticism of a sitting US President -- and fellow Republican -- remains rare.

The senator delivered a similar critique of the President's foreign policy during a speech at a security conference in Munich in February.

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McCain has been a vocal proponent of the US-Australian relationship, and his speech appeared to reinforce the belief that despite the whims of the Trump administration, Australia and the United States need each other if both want to maintain the current geopolitical order.

"Now more than ever, we Americans are counting on Australia and our allies to stick with, to encourage us to stay true to who we are at our best, and remind us always just how much is at stake," said McCain. "Our foreign friends always tend to focus on the person in the White House. But America is far bigger than that."

Reports of a tense phone call between President Trump and Australian Prime Minister Malcolm Turnbull in February -- which Trump later said were a "big exaggeration" -- sparked concerns over the future of the US-Australian relationship.

Since then, the Trump administration's isolationist direction has left some Australian leaders worried that Australia will need to readjust its policy in the Asia-Pacific region.

"There's a great sense of loss about the America that we thought underpinned the security order (and) that the America we relied on might not be there," Mathew Davies, head of the international Relations Department at the Australian National University, told CNN earlier this month.

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China

Some in the Australia foreign policy establishment worry that if the United States influence in the world begins to ebb, it will need to pivot closer to China, its largest trading partner.

McCain called that a "false choice."

"The real choice, the real question, is whether America and Australia are better off dealing with China's strategic and economic challenges together, or by ourselves," he said.

But those concerns were exacerbated earlier this year when the US withdrew from the Trans-Pacific Partnership, a massive 12-nation trade pact.

McCain called the decision "a major strategic mistake" in his speech.

"The idea that China is now the steward of our open, rules-based global economic order -- it may sell at Davos (the economic forum in Switzerland). But people in this country and this region know better," McCain said.

His comments that China is "asserting vast territorial claims that have no basis in international law" would appear to refer to China's moves in the South China Sea. Beijing has been accused of trying to claim most of the contested waters as its own territory. It's been creating man-made islands and building airfields, ports and weapons systems on them. A third of the world's maritime traffic passes through the South China Sea.

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"We (Australia and the United States) believe that when the strong trample the rights and independence of the weak with impunity, then our liberty and our sovereignty are at risk. We believe that when all peoples cannot sail the seas, and fly the skies, and engage in commerce freely, then our prosperity will suffer. We believe that when the balance of power in the world favors those bent on injustice, and aggression, and conquest, then the peace we cherish will not last," McCain said.

CNN is attempting to reach the Chinese Ministry of Foreign Affairs for comment.

Trump's tone on Beijing has softened since he and President Xi Jinping met for a summit in April. The US has rarely brought up the South China Sea issue. Following a North Korean missile launch Monday, Trump said China is "trying hard" to help diffuse tensions on the Korean Peninsula.

North Korea has shown great disrespect for their neighbor, China, by shooting off yet another ballistic missile...but China is trying hard! — Donald J. Trump (@realDonaldTrump) May 29, 2017

But as a candidate, Trump took a much harsher tone on China, accusing the country of "raping" the United States and not doing enough to rein in North Korea.

During his confirmation hearing, Rex Tillerson, his Secretary of State, likened China's island-building in the South China Sea to the Russian seizure of the Crimea from Ukraine, which prompted Western states to isolate Moscow and boot it from the G-8.