At least 300 interpreters are seeking protection in Australia as allied troops depart Afghanistan.

Scott Morrison said Australia was "very aware" of the issue and was steadfastly going through the paperwork.

The prime minister said it was a sensitive matter but one that he recognised had to be dealt with swiftly.

"We have done this before safely, and we will be able to do it again, but it would be very unhelpful for me to elaborate any further on that issue," he told reporters in Sydney on Tuesday.

"We are very aware of it and we are working urgently and steadfastly and patiently to ensure that we do this in the appropriate way as we have done on earlier occasions."

The military chief who led Australia into Afghanistan 20 years ago earlier warned vulnerable interpreters must not be left behind.

"We have a very serious obligation," retired admiral Chris Barrie told ABC radio.

"It would be unconscionable to leave these people to the mercy of the Taliban. We must do something to help them."

Mr Barrie likened the situation to the aftermath of the Vietnam war, when military supporters brought refugees into Australia before political leaders officially endorsed their arrival.

The interpreters' plight has been made all the more difficult following Australia's decision to close its embassy in Kabul due to security fears.

Mr Barrie questioned the embassy closure decision, saying it made it even harder to lodge visa applications.

"But I'm sure if we put our minds to it we could find a way around that," he said.

"I'm not sure that (closure) was a good call myself but we must not ever leave these people to fend for themselves."

The United Kingdom and the United States have both agreed to fast-track the resettlement of thousands of Afghan interpreters and their families.

Foreign Minister Marise Payne spoke about the visa issue on a recent trip to Kabul and has indicated the government is keen to support all eligible translators.

The last remaining Australian troops will depart Afghanistan by September, following America's decision to end the war before the 20-year anniversary of the 9/11 terror attacks.

Australian Associated Press