Canberra, Australia - Ex-Australian Prime Minister Malcolm Turnbull has used a speech to criticize and mock President Donald Trump, and issue a warning to leaders.

Turnbull, who served as Australia's PM from 2015 until 2018, issued a warning that the country's next leader needs to "stand up" better against Trump, even if that means facing a flood of social media abuse.

His comments come days after current PM Anthony Albanese called an election for May 5, 2025.

"They've got to be able to stand up," Turnbull told the National Press Club of Australia on Tuesday.

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"If that means they get a brickbat or a Truth Social post saying 'You're weak and ineffectual. You don't know anything about China'... If you're spooked by that you shouldn't be in the job."

As he spoke about a potential Truth Social post, Turnbull imitated Trump and repeated the word "China" in a mocking voice. The impersonation drew laughs from the crowd, who proceeded to applaud.

Turnbull also drew a comparison between Trump's stance on Canada being the US' 51st state, and Russia's views on Ukraine, claiming that Trump has similar territorial ambitions in North America.

"There's an eerie resonance between the language Trump uses about Canada and the language [Vladimir] Putin uses about Ukraine," he said. "Borders are fictional, doesn't deserve to be a separate country, and so forth."

According to Turnbull, Australia needs to stand up to the "billionaire bully" and start looking after itself, rather than relying on the US for its defense.

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He spent a long period explaining the weaknesses and failures of the AUKUS security and submarine deal, which saw his successor, former PM Scott Morrison, scrap a deal that Turnbull had signed with the French.

"Do you think, if there was an Australian version of Donald Trump, do you think that person would be tiptoeing around worrying about offending the United States?" Turnbull said.

"Of course not. He’d be standing up for Australia… and that's the challenge for our leaders."