'The line-up is huge': Australians caught up in US flight chaos

A major air traffic control outage in the US has disrupted thousands of flights, leaving Australians stranded and warnings about global flow-on impacts, including international delays.

Airlines are working to clear the backlog as US authorities investigate what caused the outage.

Australians have been caught up in widespread flight disruptions across the United States after a communications outage forced aviation authorities to ground flights nationwide.

More than 11,000 flights were delayed or cancelled, with passengers left stranded at airports across the country after the Federal Aviation Administration (FAA) issued an unprecedented ground stop.

The grounding has since been lifted, but airlines are warning it could take time to clear the backlog, with disruptions also affecting flights departing Australia for the US.

Sydney Airport said flights to the US would now resume from Mascot after being temporarily grounded on Saturday morning, and urged passengers to contact their airlines.

The disruption has affected travellers at major airports including New York's JFK, Los Angeles International Airport and San Diego.

Trish Crabb, from Adelaide, was among those caught up in the chaos after her flight from New York to Miami was grounded.

She and her husband were due to fly out of JFK Airport when they discovered their Delta flight had been cancelled.

The couple are holidaying in the US and had planned to drive from Miami to Fort Lauderdale to board a cruise.

"My husband is going to try and find us a hotel room somewhere close by, and hopefully we will be able to get a flight out at some stage," she said.

Despite the disruption, Ms Crabb said passengers appeared to be keeping their composure.

"Everyone was very calm," she said, adding most people were taking the situation in their stride.

Rivkah Brown, from Myrtleford in Victoria, was stranded at San Diego Airport after her Delta flight was cancelled.

Ms Brown had just disembarked from a cruise and was stopping over in San Diego before travelling to Las Vegas, where she was due to meet her fiancé.

She said she would now take a bus to Las Vegas instead, a journey of almost 10 hours.

"It's disappointing but it is what it is," Ms Brown said.

The FAA ordered the nationwide ground stop on Friday, local time, after communications problems affecting air traffic control centres across the United States.

US Transportation Secretary Sean Duffy said the issue was affected all Air Route Traffic Control Centres, with technicians investigating the cause.

The FAA said the decision was made because of "extraordinary circumstances and for reasons of safety".

US Homeland Security Secretary Markwayne Mullin said preliminary investigations pointed to a telecommunications outage, with no immediate indication of a deliberate attack.

The outage affected the 22 regional air traffic control centres responsible for directing aircraft between airports across the country.

At least 600 flights had been diverted, including aircraft sent back to their departure airports or redirected elsewhere.

About 11,000 flights carrying more than 1.5 million passengers had been scheduled to depart US airports after 4pm Eastern time on Friday.

Planes already in the air were able to continue to their destinations, with authorities prioritising their safe landing.

The nationwide ground stop was the first since January 2023, when a computer system failure at the FAA caused thousands of delays. It was also only the second nationwide grounding since the September 11 terrorist attacks in 2001.

Australian travellers caught up in the disruption are being urged to contact their airline or travel agent if they are due to fly within the next 72 hours.

The Australian Travel Industry Association (ATIA) says those passengers are being prioritised, while people travelling later are being asked to hold off contacting travel providers so urgent cases can be dealt with first.

Travellers should also check their airline's website or app for flight updates.

ATIA chief executive Dean Long said passengers travelling soon should contact their provider if they had not already heard from them.

"We know this is unsettling for travellers. Our members are there to help, and we are monitoring the situation closely."

The Federal Government's SmartTraveller website is telling Australians to monitor media and contact airlines for updates and to reschedule flights.

It advises travellers to exercise "normal safety precautions" in the US.