Permanent security upgrades could be imposed at Australian airports to protect travellers from terrorists after authorities foiled an alleged plot to bring down a passenger plane.
Four men remain in custody after NSW and Federal Police raided five properties across Sydney on Saturday, but the intensified security provisions began two days prior at Sydney Airport.
They've since been extended across the country and Prime Minister Malcolm Turnbull has left open the prospect of lasting changes to airport security.
"The heightened security measures at the airport, as everywhere, are under constant review," he told reporters in Perth on Monday, as crowds and queues clogged Sydney airport.
Sydney's domestic terminal 2, which handles Jetstar, Virgin and Tiger flights, appeared to be the worst affected, with passengers spilling out of the terminal doors.
"The queue now stretches outside the terminal and down the entire length of T2 at Sydney airport," tweeted one observer.
During the morning peak, there were inconsistent delays of up to one hour and passengers generally took the advice from authorities to arrive earlier.
Mr 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.
The government is not revealing any details of the alleged plot, as speculation mounts the Sydney men intended to plant an improvised bomb inside a kitchen grinder or release poisonous gas.
Opposition Leader Bill Shorten supported calls for passengers to show identification before they board flights.
"It seems to me at first blush to be a bit sensible that you know who's actually getting on the plane," he told ABC radio on Monday.
Justice Minister Michael Keenan said he didn't want to rule things in or out, "but if there was a requirement to do that to keep the Australian people safe then obviously we would do that".
Australian National University criminologist Dr Clarke Jones said the security response was a way for the government to show capability and create deterrence.
"It's a typical pattern after these sorts of acts," he told AAP.
"Whether that's justified, whether we go too far into overdrive, that's another situation."
AFP Commissioner Andrew Colvin said travellers could be confident in airport security arrangements.
"What we are doing, what you're seeing at the moment is making sure there is extra vigilance, to make sure we aren't cutting any corners in our security. This is not stagnant though and we are always reviewing what the best arrangements are."
Earlier, Border Protection Minister Peter Dutton said: "It may be that we need to look at the security settings at our airports - in particular our domestic airports - for an ongoing, enduring period."
For travellers, the new normal is a directive to arrive at airports two hours before domestic flights, and three hours before international flights.
