The Department of Foreign Affairs and Trade issued updated advice on Thursday to warn people not to travel to Hamid Karzai International Airport.

Defence Minister Peter Dutton said in question time that the security situation in Afghanistan was "dire" and deteriorating", two weeks on from the Taliban's takeover of the capital.

Mr Dutton said there were "credible threats and intelligence" about the possibility of a terrorist attack at the airport and surrounds.

"There has been advice issued by the US, the UK and Canada, New Zealand and ourselves, that people should not gather at the gates at the airport, that they should move immediately from that area and that they should not be in areas of large gatherings," he told Parliament.

Prime Minister Scott Morrison and Foreign Minister Marise Payne had earlier revealed that a further 1200 people had been evacuated overnight on four Australian and one New Zealand flights.

Almost 4000 Australians, Afghan visa holders and people from allied nations have been airlifted from chaos in the Afghan capital since the operation began more than a week ago.

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With the US' August 31 withdrawal deadline edging closer, Mr Morrison again acknowledged that some people trying to flee might not be able to evacuated.

"For more than a week now, I believe I have been preparing Australians about the difficulty of this operation and the extreme moral hazard of the environment in which we're operating," he told reporters on Thursday morning.

"I said we'll do everything we possibly can to get as many people out as safely as we can."

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