Adelaide Airport security breach that triggered main terminal ...

Adelaide Airport's main terminal has been evacuated because of a security breach, causing major disruption and flight delays.

The airport's management said the breach occurred when passengers on a regional flight entered the terminal without being properly screened.

Airport management said operations are back to normal.

Adelaide Airport says human error was behind a security breach that resulted in the evacuation of the main terminal on Monday morning.

Passengers arriving on a regional flight from Kingscote entered the main area of the terminal without going through security screening just before 11am, the airport said.

Adelaide Airport spokesperson Dermot O'Neill said about 15 flights and 1,500 passengers were delayed by up to two hours.

"Passengers that arrive into Adelaide from regional airports that are unscreened … are required to be screened before they enter the main area of Adelaide Airport," he said. 

"We take the security outcomes of Adelaide Airport very seriously."

Mr O'Neill said operations at Adelaide Airport were back to normal and encouraged passengers to check the status of their flight before heading to the airport. 

Passengers at the site are being re-screened.(ABC News: Briana Fiore)

Earlier, hundreds of people were packed into the departure floor as passengers waited to go through security screening.

One passenger wrote on social media that they were 20 minutes from departure, but were expecting a wait of several hours.

"Everyone has to leave for re-screening! Even those on planes about to depart," the person wrote.

There are major disruptions and flight delays.(ABC News: Briana Fiore)

Airport passenger Roy Abraham said he was moments away from boarding when the evacuation began.

"I was probably going to board in about a minute's time and then this happened so there were probably people already on the plane who had to get off to," he said.

"All the pilots had to get off the planes as well, so there was probably thousands of people behind me.

"We weren't really sure what was going on, there was a lot of chatter as you can imagine."

A similar breach at the airport occurred in 2021, and Mr Abraham said quick thinking ensured him a prime spot in the queue.

"When the call first came through, they said there's been a security breach, please evacuate the airport immediately," he said.

"Because it's happened to me once before, I made a quick beeline out of security as quick as I could so I could be at the front of the queue again but it took them a while to get everyone out of the airport.

"It could be a couple of hours, it's lucky I don't have a connecting flight."

Passenger Caroline Jessen (left) was evacuated from the main terminal before her flight.(ABC News: Briana Fiore)

Adelaide woman Caroline Jessen said she was just about to board her flight to Sydney when she was evacuated. 

"We had an announcement just saying we had to evacuate the terminal and we heard that a couple of times and then we all just started moving out," she said.

"It was very orderly, very safe and good."

One passenger, Dan Thompson, said he was in the airport bathroom when the announcement came over the loudspeaker.

Dan Thompson was evacuated from Adelaide Airport on Monday morning.(ABC News: Briana Fiore)

"It was a bit of a shock," he said.

He was going to Melbourne and hoped he would still get there on time.

"I guess these things happen."

Mount Barker local Lindsay Campbell, who arrived when the situation was unfolding, said communication from the airport had been good.

"It was a bit of a shock when I walked in to see what was going on, but I've been on the tail end of it.

"It's just one of those things, you grin and bear it."

Lindsay Campbell says the evacuation was a shock.(ABC News: Briana Fiore)