CANBERRA - Australia's High Commissioner to Britain and former Foreign Minister Alexander Downer Wednesday backed calls for China to join the Trans-Pacific Partnership (TPP) free trade deal, following US President Donald Trump's decision to withdraw from the agreement.

Downer, Australia's longest serving foreign minister, is the latest in a strong chorus of Australian support for China to join the deal, after Prime Minister Malcolm Turnbull and Trade Minister Steve Ciobo backed China's entrance into the TPP.

On Wednesday, Downer, who is accompanying Treasurer Scott Morrison on a diplomatic mission in Britain, said while Trump's decision was "disappointing", the remaining 11 nations shouldn't "throw in the towel".

"Our point is why would you give up? We want to see what else we can do," Fairfax Media quoted Downer as saying.

The respected diplomat said if the TPP nations decided to approach another nation to enter the agreement, China would be a "desirable" ally.

"'Twelve minus one' is one possibility, maybe adding other countries like Indonesia and China to the TPP and get that ratified, there are all sorts of options and we're not ruling any of them out at the moment," Downer said.

"Basically from Australia's point of view we want to reach out and achieve free trade with as many countries as we can, we already have a free trade agreement with China."

Downer's sentiments echo that of the government. Prime Minister Malcolm Turnbull on Tuesday said there "certainly is the potential for China to join the TPP", while Trade Minister Steve Ciobo said China was most welcome if it so desired.

"What China decides to do is ultimately, of course, a decision for China," Ciobo said.