Terrorist attacks on Australia are an ever-present likelihood despite national security forces' best efforts to prevent them, says Australia's Prime Minister (PM) Malcolm Turnbull.

Turnbull made the comments, published on his official website on Tuesday, at the conclusion of the two-day G20 leaders summit in Antalya, Turkey, which has been hijacked by talk of the atrocities carried out on the French capital of Paris on Friday.

"We recognize risks exist, attacks are possible," Turnbull said in a statement released in Canberra on Tuesday.

"Attacks in this environment are likely to happen in the future."

After a long night of discussions, Turnbull said all leaders had banded together and recommitted to an "utterly united" push to defeat terrorism in all its forms.

Turnbull said he had been in contact with chiefs from Australia two major terror-combating authorities, the Australian Security Intelligence Organization (ASIO) and the Australia Federal Police (AFP), since the Paris attacks which has left 132 people dead.

On the advice of those agencies, Turnbull has chosen not to update Australia's terror threat alert -- a status grading the likelihood of an attack -- from likely to imminent.

Turnbull noted that the G20 summit, primarily an economic conference, had afforded him a great chance to present the historic Chinese-Australia Free Trade Agreement (ChAFTA) to fellow members.

"We have had very good discussions about infrastructure, particularly urban infrastructure, about the importance of free trade, the entering into by Australia and China of the Australia and China Trade Agreement for example has been widely welcomed," he said.

Turnbull said the Australian government was still "seeking speedily to finalize all of the ratification process so it will come into force", and he hoped the arrangement would strengthen ties between the two nations.