Sydney  -  Australian authorities Sunday defended their decision to shut Perth's international airport terminal for 12 hours after a security alert that proved unfounded.

The terminal was cleared Saturday after baggage handlers decided unaccompanied freight on a Malaysia Airlines flight from Kuala Lumpur was suspicious. It took police nine hours to X-ray the cardboard boxes and rule that they were harmless.

"It was a major operation, it was an operation that caused ... considerable inconvenience to the travelling public, to the staff at the airport, to government agencies that responded, and that's regrettable," John McRoberts, assistant commissioner of counter-terrorism and state protection, told national broadcaster ABC.

"But I think people ought to take some comfort in the fact that the safety of everybody was of paramount concern to us."

More than 3,000 travellers were evacuated from the terminal and held at an exclusion zone two kilometres from the airport buildings.

McRoberts declined to say why the packages were suspicious or what was in them. They were part of a consignment for someone in Perth. (dpa)