James Grubel was AAP's chief political reporter covering then-prime minister John Howard's first meeting with then-US president George W Bush in Washington DC for the 50th anniversary of the ANZUS treaty.
Day one of the visit had gone smoothly.
Day two was to start with a press conference before the prime minister was to deliver a speech later in the day.
News of two planes striking the World Trade Centre in New York had reached the press pack in Washington moments before Mr Howard spoke to the media.
"It had become a little bit more obvious that this was a serious event," Mr Grubel told AAP.
"The prime minister gave his condolences. And still, at that stage, we were thinking the day was going to go ahead as normal."
But as the curtains were opened in the Willard Hotel at the close of the press conference, smoke was billowing from across the Potomac River.
A third plane had struck the Pentagon just 5km away.
The gathered journalists were forced to evacuate, walking one mile down the road to the Australian embassy as thousands of people scrambled to get out of the city.
"The whole of Washington was in gridlock," Mr Grubel said.
"There were armed police and soldiers on the corners ... I think every building in Washington and everybody was evacuating.
"It was a totally different city to the one that we'd been wandering around in for the past couple days."
The mood in the Australian embassy was sombre, according to Mr Grubel, as journalists continued writing for the media back home.
"The magnitude of this awful event slowly, slowly hit, and you had to occasionally stop yourself and just focus on what you were doing and try and put it out of your mind so you could write about it clearly.
"Otherwise, you'd kind of get a bit caught up in it. It was very unclear whether there were going to also be attacks on on London, on Paris and Sydney, on Canberra."
Ten Australians were among the almost 3000 people who died when al-Qaeda militants hijacked four planes on September 11, 2001.
The hijackers flew two planes into the twin towers at the World Trade Centre in New York and one into the Pentagon just outside of Washington.
The fourth plane crashed into a field in rural Pennsylvania.
John Howard decided to invoke the ANZUS treaty three days later on the advice of his foreign minister. If the United States was under attack, Australia had an obligation to send troops.
It was a poignant end to an event which Mr Grubel says has rippled out to the present day.
"Now with AUKUS, we're still going through these issues and these debates about our national security," he said.
The shift in political rhetoric to security and defence bolstered support for the Liberal government heading into the 2001 federal election which it ultimately won.
A quarter of a century on, Mr Howard said the lesson to be learnt was in being vigilant to the world around us.
"We must be alive to the threats that face us but not live in constant fear," Mr Howard said in a statement.
Prime Minister Anthony Albanese, who was a Labor backbencher at the time of the attack, said it remained a harrowing anniversary a quarter of a century on.
"Alongside the many Americans who lost their lives, were people from nations across the world, 10 Australians among them," Mr Albanese told the parliament on Thursday.
"America was shaken to its core, but it did not yield. It did not break."
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