Former prime minister John Howard (Image: SBS News)

Days after the final Australian troops left Afghanistan, the man who first sent them there 20 years ago says the government must grant visas to Afghans who helped the defence force (ADF) during our longest conflict.

Former prime minister John Howard told SBS Australia has a "moral obligation" to provide asylum to the thousands of people who were critical to Australia's war effort.

It's a major intervention from a Liberal elder statesman, and one which will put further pressure on the Morrison government to fast-track the evacuation of Afghan translators, local staff and their families as the Taliban advances through the country. And it highlights growing concern, including from within government ranks, that a situation everyone agrees is a humanitarian crisis is getting out of Australia's control.