Travellers may have to get used to long delays at Australian airports after the government announced permanent security upgrades to protect passengers as authorities detain four men over an alleged plot to down a passenger plane.

Border Protection Minister Peter Dutton warned on Monday that the government may have to reconsider the security procedures at airports “for an ongoing, enduring period”.

Australian Federal Police Commissioner Andrew Colvin also flagged, possible long-term changes saying security measures were “always” under review.

Passenger, hand and checked luggage screening has been ramped up at all Australian airports after counter-terrorism officers arrested four Sydney men accused of plotting to bring down a plane departing Sydney.

The new measures caused chaos and huge delays at major airports over the past two days, with Sydney’s domestic Terminal 2, that handles Jetstar, Virgin and Tiger flights, seemingly the worst affected, with queues stretching well outside the terminal doors on Monday.

Prime Minister Malcolm Turnbull thanked travellers for their patience but shut down any suggestion of a so-called “terror tax” to better resource airports to deal with heightened security.

“No, no,” he said when asked about it.

Passengers at Sydney Airport face long waits due to new security measures. Photo: Getty

But some security experts have called for all domestic travellers to be made to produce photo identification when checking in.

The government has refused to reveal details of the alleged plot, as media speculated that the Sydney men intended to variously plant an improvised bomb inside a meat grinder or release poisonous gas inside an aircraft.

All it will say is that the four – believed to be two fathers and their sons – planned to use a “non-traditional” device and had “an Islamist, extremist terrorist motivation”.

Meanwhile, domestic passengers are being told to arrive two hours before flight departures, and international passengers three hours before, to allow for tougher checks including more intensive screening for explosives.

Domestic passengers are also being advised to limit luggage to carry-on only where possible.

Police at the Surry Hills address where two of the men were arrested. Photo: AAP

Beefed-up security is just ‘window dressing’: expert

But one security and terrorism expert has told ABC radio that the increased passenger security in force at Australian airports on Monday, was just “window dressing”.

Chief executive of Homeland Security Asia/Pacific Roger Henning said airport security scanners do not pick up every threat and that no scanner can detect plastic explosives.

“The plot that has unravelled in the last couple of days, probably would’ve been stopped if they were using a metal kitchen object as part of their [explosive device],” he told RN Breakfast.

“But there are other ways of blowing up aeroplanes and they’re certainly not covered by anything the Australian Government or agencies have done to date.”

He said it was “ridiculous” for politicians to know of the loopholes and to still say scanners were the answer, saying human intervention was the best weapon in the fight against terror.

“Human intervention is the best weapon against terrorism because people are likely to appear out of character.

“The only real difficulty with this in my experience is that a determined bomber, or suicide bomber, usually exhibits serenity.”

– with AAP