Sydney Airport's boss says "inexperienced" travellers have contributed to a "perfect storm" causing major delays at Mascot.
People have reported languishing in queues for hours to pass through security during the past two days.
Footage from the airport has shown snaking lines stretching through and outside terminals.
Some planes have had to be held back to allow passengers to make their flights as people flocked to travel for the Easter school holidays.
On Friday morning, crowds swelled so large at Terminal 2 that the distinction between lines was unclear, causing confusion for travellers.
Police officers began directing people to the most appropriate line as people sought to work out where they should go.
Geoff Culbert, Sydney Airport's chief executive, issued an apology to passengers, saying COVID-19 was at the root of the issue.
"We're facing a perfect storm at the moment," he said.
"Traffic numbers are picking up, travellers are inexperienced after two years of not travelling, and the close contact rules are making it hard to fill shifts and staff the airport.
"We encourage everyone to get to the airport early and thank everyone for being patient as the industry gets back on its feet."
Passenger George Wong said he arrived to find "crazy" lines and he was worried he would miss his flight.
"It's really confusing and we don't know what to do," he said.
"We haven't seen this for ages, particularly in a domestic flight. We didn't know we had to come so early."
A frustrated Adam Cosgrave said staff had given him mixed instructions about where he needed to go to make his flight to the Gold Coast.
"It is absolute chaos," he said.
"I've been waiting here for about 3 hours and it's just not good enough."
Des Kane said he had been lining up for more than an hour to get through immigration before boarding a flight to London.
He said staff had been helpful and ushered people to the front of queues if they were in danger of missing flights.
"Flights are being held and the queue has started moving now," he said.
"I've been in the queue for an hour and probably will be for another 30 minutes but it is moving now."
