Turnbull sworn in as Australia's 29th PM

Canberra: Former communications minister Malcolm Turnbull was sworn in as Australia's 29th prime minister on Tuesday and praised the man he ousted as a "great Australian".

He was sworn in by Governor-General Peter Cosgrove and pledged his allegiance to Britain's Queen Elizabeth-II at a hastily organised ceremony at Government House in Canberra earlier in the day, ABC reported.

Turnbull took the oath of office, with deputy Liberal leader Julie Bishop and his wife among the assembled supporters.

He staged a leadership coup on Monday afternoon, culminating in a Liberal Party room vote that he won 54-44.

He has pledged to run a more collegiate, cabinet-focused government and to hold the line on the existing same-sex marriage and climate change policies that were endorsed by Tony Abbott as prime minister.

Abbott delivered his own speech, conceding he had been ousted as a first-term prime minister after just two years in office.

He has partly blamed internal "white-anting" and "character assassination" in the media for his demise, but promised not to "wreck" his Government in retribution.

Turnbull began his first Question Time as prime minister by arguing his predecessor should be recognised for his achievements.

"Our nation, our parliament, our government, our party - our parties, the Coalition - owe Tony Abbott an enormous debt of gratitude for his leadership and his service over many, many years," he said.

"He led us out of opposition and back into government."

"Tony has discharged his role as prime minister - be it as leader of the opposition - with enormous distinction and achievement," he added.

Turnbull said the free trade agreements clinched by the Abbott government were an example of success.

He also congratulated Abbott for his border protection policies, arguing they allowed the government to provide for an additional 12,000 Syrian and Iraqi refugees.