Prime Minister Malcolm Turnbull has said counter-terrorism agencies foiled a plot to "bring down" a plane in an Isis-inspired terrorist attack and Australian airport security measures across the country have been heightened as a result.

Four men were taken into custody on Saturday night when heavily armed counter-terrorism officers raided four Sydney properties over an alleged plot that reportedly involved blowing up an aircraft.

Mr Turnbull said increased security measures have been placed on all Australian airports.

"Those travelling should go about their business with confidence," he said.

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TV footage shows a man with a bandage on his head and draped in a blanket being led away by authorities. Photo: 7 News

"But the Office of Transport security has advised that security screening will take longer and travellers should arrive at terminals at least two hours before flights to allow ample time for screening.

"They should limit the amount of carry on and checked baggage as this will help to ensure security screening is efficient."

Australian Federal Police, NSW Police and the domestic spy agency ASIO jointly carried out the major counter terrorism operation in Surry Hills, Lakemba, Wiley Park and Punchbowl.

TV footage shows a man with a bandage on his head and draped in a blanket being led away by authorities.

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Prime Minister Malcolm Turnbull has been briefed on the progress of the operation by security agency heads. Photo: AAP

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