The Australian Federal Police has increased security operations and patrols at the country's major international airports in the wake of the deadly attack on Brussels Airport on Tuesday.
"Security measures at these airports are multi-layered and may involve armed mobile, canine and foot patrols, static guarding as well as specialist response armed capability," an AFP spokeswoman said. "A range of technical measures such as extensive CCTV also support these security measures."
Prime Minister Malcolm Turnbull on Wednesday morning told ABC Radio the AFP had advised security levels at Australian airports were "appropriate" and had not been increased. However, it was later clarified he was referring to the overall threat level rather than specific measures at airports. 
In Australia, Border Force personnel had planned strikes over the busy Easter travel period, including a 24-hour stoppage at all international airports and cruise terminals on Thursday that was expected to cause delays for travellers arriving and departing Australia. But the Community and Public Sector Union on Wednesday said it would postpone the planned strike action after calls from Mr Turnbull to do so. The union has now planned rolling strikes from   March 29 to   April 4.
The Brussels attack occurred at the airport check-in area where no one needed to present a boarding pass or identification to be present.
When asked if there should be tighter security at the entrances to Australian airports, Mr Turnbull said he would be taking advice on that.
"We have not got advice on any changes in that regard at this stage. But every single one of these attacks, wherever it is anywhere in the world, we learn from and we make adjustments and we reassess the circumstances in light of the new intelligence we receive," he said.
Contingency plans
Australian Airports Association chief executive Caroline Wilkie said industry and government agencies were in dialogue about appropriate measures that could be put in place to respond to plausible threats.
"The Government, airports and airlines have for some time worked on contingency plans that can be effected quickly should the security threat level increase as a result of clear intelligence from government agencies," she said. "A strong, visible AFP presence at major airports will continue to support the multi-layered security measures in place to help mitigate threats."
The Brussels attack was not the first time there had been a major incident at a non-secure part of an airport. In 2011, a suicide bomber killed 37 people and injured 173 at the arrivals hall at Moscow's busiest airport, Domodedovo International.
In 2013, there was a shooting in Terminal 3 at Los Angeles International Airport that killed a security officer manning a checkpoint and wounded several others. In 1985, there were twin terrorist attacks at Rome and Vienna airports that killed 19 people at check-in counters for Israel's El Al Airlines.
Australia, like most countries, does not require boarding passes to access non-secure areas of the airport such as check-in and arrivals halls. For domestic flights, passengers can reach secure areas and board aircraft without showing identification, although they do need to pass through security scanners.
Extra checks
John Kendall, director border and national security program, Unisys Global Public Sector, said in some countries there were extra checks done before reaching the check-in area. 
"In India, when you come into an airport you are required to show a printed copy of [your] itinerary," he said. "There are some places that have experienced bombings like the Philippines where they do a full scan of baggage before you are able to enter the terminal itself. The challenges are [that] there are very few airports set up to handle that sort of thing. In the Philippines, you get used to queueing on the sidewalk."
However, Mr Kendall said just showing identification or a copy of an itinerary was not enough because those could be forged and it would be fairly useless if they were not checked against a watchlist. He said the use of biometrics, such as fingerprints, facial recognition or iris scans, would probably be required for more useful checks.
Airports Council International Europe said the possible adoption of additional security measures and checks on people entering non-secure parts of the airport, such as check-in counters, could prove disruptive and might actually create new security risks. 
"By displacing the gathering of passengers and airport visitors to spaces not designed for that purpose - such measures would essentially be moving the target, rather than securing it," the trade organisation said. 
"It is worth keeping in mind that the atrocities committed [on Tuesday] are part of a series of attacks that have hit several locations in the past six months including Paris, Ankara and Istanbul. These attacks are not limited to disrupting our transport systems, but are clearly about threatening our entire way of life by targeting other public spaces including places of social gathering and entertainment."
Airports, however, are on edge after the Brussels attacks. Denver Airport evacuated a section of its main terminal on Tuesday local time to investigate a possible security threat. London Heathrow said police were providing a "high visibility presence" at the UK's major hub in the wake of the Brussels attacks.