'Incredibly inconvenient': Flights delayed after security breach at Adelaide Airport

A security screening failure has led to thousands of people having to evacuate Adelaide Airport's main terminal and 15 flights being delayed.

Sirens forced crowds to leave the terminal and passengers who had already boarded to disembark a plane about 11am ACST (11.30am AEST).

The airport said the security breach was "understood to be the result of passengers arriving on a regional flight entering the terminal without being adequately screened".

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A total of 15 flights were then delayed, with passengers stuck in the terminal foyer for two hours as the breach was investigated.

"We were literally boarded and ready to go to Canberra and we all had to come off, so we've been sitting here waiting," Russell Mankervis told 9News.

"It's incredibly inconvenient and very annoying."

Once security screening resumed, children and passengers requiring assistance were given priority.

The airport apologised to passengers on social media:

"We apologise to our customers impacted this morning and appreciate their patience and understanding," it said.