A security breach at Sydney Airport was caused by a passenger concentrating on his iPad and not on where he was going.

A security scare at Sydney Airport that delayed hundreds of passengers was caused by a passenger concentrating on his iPad and not on where he was going.

Passengers were evacuated at Sydney Airport on Saturday morning after the man accidentally left the secure area of Terminal 3, used for domestic flights, and re-entered through the exits without going through the proper security clearance.

The man was distracted by his iPad and not paying attention to where he was going, a spokeswoman for Qantas said.

Security officials saw the incident on CCTV cameras and decided to re-screen all passengers in the terminal as a precaution.

That caused delays of over an hour for eight flights, with more than 1000 passengers.

Many of those passengers were on their way to Melbourne to watch the Sydney Swans play Hawthorn in the AFL grand final.

The incident comes amid a heightened terror threat level in Australia and follows counter-terrorism raids in Sydney and Brisbane.

No other domestic or international terminals were affected by the breach, a Sydney Airport Corporation spokesman told AAP.