Spy agency ASIO has briefed airlines and airports about the US warning and Qantas said it was in regular contact with intelligence and security organisations.
In the US today, President George W Bush said there was a 'real threat' of new al-Qaeda attacks.
'The threat is a real threat ... We don't know when, where, what,' he said at a news conference.
'We have got some data that indicates that they would like to use flights, international flights for example. I'm confident we will thwart the attempts.'
Mr Downer said it was unlikely flights from Australia would be used for terrorist attacks in the US or Europe because Australia was so far away.
'If you were to hijack an aircraft in Australia and fly it all that way it would have to refuel on the way, it would be a complicated situation,' Mr Downer said.
'Seems to me on the face of it, a little unlikely that Australia would be the ideal source.'
Mr Downer said Australia had a high level of airline security, with air marshals travelling on many flights and baggage being carefully screened at airports.
'Ever since September 11 2001 we've increased very substantially the degree of security for aircraft going overseas, as well as domestically,' he said."
How quickly they turn. As soon as the domestic needs of the two governments diverge, suddenly Australia and the US do not agree on aviation intelligence nearly as much as they do on the WMDs. On the other hand, I find it more than faintly worrying that I am in agreement with Lord Downer of Baghdad.
The US claim is that planes might be hijacked in Australia for suicide attacks on the US east coast. They do not say whether the hijacked planes would be flown to the US east coast via Europe (flight time around 30 hours) or by way of the US west coast (only around 22 hours but it does involve overflying the entire continental US. With lead times like that even the Bush administration could possibly get its air defence system working in time to intercept. They could even get Air Force One and George Bush safely aloft and still scramble interceptors.