Would-be commuters were left stuck at check-in early on Friday morning after a technical issue resulted in the security screening being unable to open.
At about 8:30am, Sydney Airport reported they had resumed processing passengers as normal and were "working hard to catch up on delays", a Tweet from the company said.
The problem is preventing passengers from being processed through security causing huge queues to form throughout the affected terminals.
Inbound flights and Qantas flights from T3 remain unaffected.
"The safety and security of our passengers is our number one priority and we are pleased to say that all systems are operating as normal", an airport spokesman said in a statement.
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Virgin Australia flights were also recovering from significant delays, which included two cancellations.
At around 6:30 AM on 25 September, Airservices Australia said on social media it was "working to rectify the issue while managing traffic safely" as boards at the airport listed flights as "delayed due to ATC radar failure".
"Please contact your airline for flight status".
All planes yet to take off were instructed to disembark so passengers could be re-screened.
It affected systems including the airport's CCTV, meaning passengers could not be screened for about two hours.