A SECURITY breach forced the lockdown of Adelaide Airport - prompting an evacuation and delaying hundreds of passengers.

An airport spokesman said CCTV had captured two males forcibly opening two security doors, about 5.30pm, leading to the terminal into lockdown.

Passengers in the departure lounge were told of the security breach and had to be evacuated from the airport. All passengers were then re-scanned, causing delays of up to an hour.

The spokesman said the airport couldn't be satisfied the two people hadn't brought prohibited items into the airport or passed them to another person.

He said the matter was being investigated by Australian Federal Police. The Advertiser understands passengers on a Sydney flight were kept waiting for about 40 minutes before they were allowed to disembark. Other incoming flights were largely unaffected.

Romina Martiniello, 20, from Melbourne, was waiting in the departure lounge to board her flight home when she was told of the security breach.

Ms Martiniello said she and her friends were told to evacuate the airport. "We were very annoyed, we just wanted to go home," she said. "I guess it's better to be safe than sorry."

Passengers were allowed back through the screening area about 6.15pm and were cleared within an hour.

An AFP spokeswoman said it was making inquiries and could not comment further.