Adelaide Airport was temporarily evacuated on Monday afternoon because of a security issue, which has led to flights being delayed after major queues formed in the main terminal.
The evacuation began about 2:00pm, after a system failure allowed people to enter the terminal without being properly screened.
The Australian Federal Police (AFP) said a "small number of people" passed through a "non-functional" security detector, describing the problem as a "minor systems outage".
As a precaution, all passengers and staff were evacuated from the terminal while a security sweep was done.
Passengers had to disembark from planes and huge queues formed as airport security began scanning them for a second time.
The airport is continuing to operate, but a spokesperson said some flights have been delayed as a result.
"All customers were moved out of the sterile area [and] a security sweep conducted.
"It is anticipated there will be some flight delays and passengers should check with their airlines for their flight status."
Some passengers were left frustrated by the situation, saying communication had been poor.
One passenger, Deanne, said she was ready to board when she was alerted to the problem, but information since then had been "very minimal".
"They announced there'd been a security breach and we all had to leave the airport and re-enter screening once they'd got everyone out," she said.
"I think we've been outside 30-45 minutes, my plane was meant to go at 2:55pm, and it's now 3:45 or something, so yeah, big delay."
Another person who was preparing to see off her sister said she was a "little bit scared because we don't know what's happening".
A similar incident occurred at the airport in December 2019, when the main terminal was evacuated due to what authorities described as a "security fault" that required passengers to be re-screened.
