Malcolm Turnbull is hopeful of Australia being one of the first countries to seal a free trade agreement with the UK post-Brexit.
Britons voted in June to leave the European Union, which means its trade links with other countries need to be reset.
British Prime Minister Theresa May, who is at the G20 in China with Mr Turnbull, said the summit was an opportunity to talk to world leaders about trading arrangements.
Mr Turnbull has had an initial conversation with Mrs May about the FTA and may get a chance for further talks over the two days of the summit.
"Looking at free trade, we've already seen in some of the early conversations I've had with some of these leaders, they're interested to talking to us about trading arrangements - the Australians for example," the British leader said.
Mr Turnbull told reporters in the eastern Chinese city of Hangzhou on Sunday he was on a "unity ticket" with Mrs May on the FTA.
"We are well advanced," he said.
"We've got things moving towards having a free trade agreement with the UK ...we are enthusiastic and supportive."
He said technical support was being provided to Britain because the country had not negotiated a trade deal for a long time.
May said on Sunday she wants to talk to fellow leaders "about the opportunities that we can develop between the UK and other countries" at the summit.
"Looking at free trade, we've already seen in some of the early conversations I've had with some of these leaders, they're interested to talking to us about trading arrangements; the Australians for example."
