Malcolm Turnbull has assured Australia its government remained strong despite an internal party revolt that made him the nation's fourth leader in little more than two years.

The former communications minister was sworn in as Australia's 29th prime minister after a surprise ballot of his conservative Liberal Party colleagues voted 54-44 on Monday night to replace prime minister Tony Abbott only two years after he was elected.

Mr Turnbull's elevation has cemented a culture of disposable leaders as the new norm in Australian politics since the 11-year tenure of John Howard ended in 2007.

The new Prime Minister said: "There's been a change of prime minister, but we are a very, very strong government, a very strong country with a great potential and we will realise that potential working very hard together.

"This is a turn of events I did not expect, I have to tell you, but it's one that I'm privileged to undertake and one that I'm certainly up to."

Shortly before Mr Turnbull was sworn in, a grim-faced Mr Abbott spoke for the first time since his sudden ousting, warning the persistent volatility in Australia's government could hurt the nation's standing on the global stage.

"Australia has a role to play in the struggles of the wider world: the cauldron of the Middle East and security in the South China Sea and elsewhere," Mr Abbott said.

"I fear that none of this will be helped if the leadership instability that's plagued other countries continues to taint us."

He did not say during his speech whether he will quit politics but promised he would not destabilise the new prime minister.

Mr Turnbull, a 60-year-old former journalist, lawyer and merchant banker known for his moderate views, was party leader for two years before he was ousted in 2009 by Mr Abbott by a single vote in a similar leadership ballot.

Mr Abbott, a 57-year-old former Catholic seminarian, has been described as the most socially conservative Australian prime minister in decades, while Mr Turnbull is considered not conservative enough by the right wing of the party.

Mr Abbott acknowledged his government had not been perfect, though he blamed the poll-heavy culture of modern politics for the frequent upheaval in the nation's leadership.

"We have been a government of men and women, not a government of gods walking upon the earth. Few of us, after all, entirely measure up to expectations," he said.