Parts of Terminal 1 at Frankfurt airport have been cleared after a passenger entered the airside part of Germany's largest airport without fully completing the security check, the airport operator said on Wednesday.

"The federal police therefore cleared Piers A and A+ and passengers will undergo the security check again," Fraport told Reuters.

The spokeswoman for Fraport added the breach would lead to flight delays at the hub, German airline Lufthansa's main base.

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