A sombre ceremony at the Australian War Memorial has commemorated 20 years since the September 11 US terror attacks and the defence force efforts since.
The Last Post Ceremony late on Saturday afternoon was off limits to the public amid Canberra's COVID-19 health orders, and live streamed through the Memorial's social media FaceBook and YouTube platforms.
It also honoured "the 39,000 Australian Defence Force personnel who served in Afghanistan and the Middle East region over the past 20 years".
A vale was delivered by Regimental Sergeant Major of the Australian Army Warrant Officer Grant McFarlane for those currently listed on the Afghanistan panel of the Roll of Honour.
Wreaths were laid during the ceremony on behalf of the prime minister and opposition leader.
Australian War Memorial Director Matt Anderson said: "Today, we remember the terrorist attacks of 11 September 2001, and those who have fallen as a result.
"We commemorate those listed on the Roll of Honour, and we acknowledge with thanks all who served in our longest war. At a time when many of us cannot yet gather in person, it has never been more important to gather in spirit."
In Brisbane, landmarks including the Story Bridge were lit in red, white and blue to remember the almost 3000 people, including 10 Australians, plus thousands injured in the attacks.
"It was a time when we saw both the worst and the best of humanity," Prime Minister Scott Morrison said in a statement on Saturday.
"Amid the devastation, we saw acts of love, great bravery and sacrifice."
Former prime minister John Howard was in Washington at the time of the attacks.
He doesn't believe al-Qaeda has the capacity for such an attack these days, but said there is the prospect of a similar organisation "regenerating" now the US and partners have pulled out of Afghanistan.
"Terrorism has never gone. It is an ever-present threat," Mr Howard told a forum this week.
"The best weapon we have against terrorism is timely intelligence."
Having been ushered to a bunker beneath the Australian embassy, the next major decision was how to respond to the attacks.
"I certainly have no regrets about committing our forces to help the United States get rid of al-Qaeda - it was the right thing to do and it had overwhelming support in Australia," Mr Howard said.
That day, 19 al-Qaeda militants hijacked four planes, flying two of them into the twin towers of the World Trade Center in New York and one into the Pentagon just outside Washington.
A fourth plane crashed in a field in rural Pennsylvania.
"Despite the pain inflicted on that day, the terrorists ultimately failed in their attempts to crush our resolve and change our way of life," Mr Morrison said.
An inquiry that followed the attacks pointed to a failure to fully understand an attack was imminent.
Australia is one of the Five Eyes intelligence partners with the US, UK, Canada and New Zealand.
Mr Morrison said the anniversary was an opportunity to "commit ourselves to continue to stand with our partners and our allies - especially this day, our great friend and ally the United States - as we work together for a world that favours freedom".
"We re-dedicate Australia to the cause of peace and freedom and to the constant vigilance required to deny the threat of terrorism in all its forms."
Labor leader Anthony Albanese said the memories of September 11 will never fade.
"We knew in our hearts then that our great friend and ally, the United States, would not be broken. We also knew that the world would never be the same again," he said.