International travellers were hit with significant delays across Australian airports after a system issue took down the country’s nationwide passport system on Sunday.

As long queues built up at Melbourne Airport (Tullamarine) around midday Sunday, Australian Border Force (ABF) said it had experienced a nationwide system issue affecting “all inbound and outbound passengers”.

“ABF is currently processing passengers manually”, Melbourne Airport told travellers Sunday afternoon.

“We are currently prioritising flights to manage passenger flows as we work to ease congestion.”

Delays were also observed across Sydney and Brisbane airports, with queues reportedly bleeding out of departure zones as staff resorted to manual processing.

Information Age understands the outage was not related to a cybersecurity issue, while an ABF spokesperson confirmed the matter “remains under investigation” as of Monday.

“ABF experienced a technical system outage, impacting passengers nationwide on Sunday 30 November,” it said.

“The issue was quickly resolved at all airports and all systems are back online.

“We wish to thank travellers for their patience during this time.”

Notably, a similar ABF system outage caused lengthy queues for Sydney and Melbourne airports in November last year.

Mayhem in Melbourne

Travellers in Melbourne appeared to be most affected by the outage, which impacted the airport for approximately two hours between midday and 2pm AEDT Sunday.

Lengthy queues were observed for international arrivals, along with numerous delays for departing international flights.

Some travellers were meanwhile made to wait on the tarmac after landing.

“Been waiting on the tarmac for about 20 minutes now returning from NZ,” said Reddit user Flayvuhh.

“They won’t let us in due to the passport system [being] broken, said it could be a while longer.”

Other travellers were reportedly told to wait four hours before the airport’s delays would be resolved.

Notably, the outage followed an incident on Friday where a fire at the airport caused flight delays and forced droves of travellers to evacuate from the airport’s Qantas terminal.

Sydney and Brisbane backed up

ABC News reported Melbourne and Sydney airports were most affected by the passport system outage, though Information Age understands ABF staff in Sydney managed to stop manual processing after just one hour.

“During the outage, we deployed additional staff to the terminals to assist passengers and bring them forward in order of flight priority,” a Sydney Airport spokesperson told Information Age.

“We would like to thank passengers for their patience.

“The issue is now resolved.”

A Brisbane Airport spokesperson said passport systems were similarly impacted for “approximately one hour”.

Just two flights to Auckland and Hong Kong had been delayed before operations were back to normal, though passengers reported notable congestion at the airport’s international terminal.

“I've literally just come from this in Brisbane. What a s*** show,” said Reddit user morris0000007.

“Hundreds of people stuck behind barriers after going through first scanner. People started to get a [bit] crushed together.

“People standing to get angry and yelling [sic]. Hundreds backing up. Could have gotten very ugly.”

Adelaide International Airport was meanwhile unaffected by the issue given the airport serviced just one international flight in the leadup to the outage.

The latest ABF outage arrived some two months after European airports suffered hundreds of delays following a ransomware attack against boarding software provider Collins Aerospace.