Australian PM Malcolm Turnbull alleged that "he would negotiate free trade agreement" with Britain at G20 meeting.
At G20 meeting, Mr Turnbull's remarks in China comes after Japan and the United States had issued notices to Britain over its status as an exchanging accomplice when it leaves the EU.
Australia was beforehand broadly anticipated that would be among the principal nations to consent to an arrangement with Britain as Mrs May looks for another worldwide financial part for the UK.
Talking after a bi-horizontal gatherings, Mr Turnbull said that Britain and Australia are "incredible companions" as he vowed to give "all the backing and help that we can" with Brexit.
He said: "England's made an extremely groundbreaking and notable decision to leave the European Union and we have as of now been occupied with talks with you about what the organized commerce courses of action may look like after that.
"Australia is resolved to furnish Britain with all the backing and help that we can. We are such incredible companions, such solid associates. (There) couldn't be two nations with nearer bonds."
Mrs May said: "It is a notable choice for British individuals. It will be a perplexing and testing process leaving the European Union. "In any case, I'm clear that it doesn't imply that we will be internal looking.
"Truth be told, we need to be considerably all the more outward-checking out the entire of the world. Furthermore, clearly, Australia, with our longstanding ties and our cozy relationship, will be one of the primary nations will look to."
England's choice to leave the EU in a June choice sent shockwaves around the globe monetary markets.
Albeit late monetary information has shown the British economy has not endured as much as some anticipated, the way toward tearing itself far from the 28-nation European alliance is likely hurl impressive difficulties.
Japan on Sunday cautioned Britain that its banks, auto makers and pharmaceutical organizations may leave the UK for Europe if Brexit prompts the loss of duty facilitated commerce.
A Government team distributed a 15 page rundown of requests from organizations and cautioned that Britain may turn into an inexorably "ugly" place for business.
It came as Barack Obama said he trusts Britain wasn't right to vote to leave the EU and recommended it is still at the "back of the line" for another exchange bargain.
The US President utilized a joint public interview with Theresa May to caution that while he wouldn't like to "rebuff" Britain there is a danger that the exchanging relationship could "disentangle".