A security breach at an airport has caused inconvenience to travelers affected at the time of the incident.

Hundreds of passengers were asked to evacuate the Qantas domestic terminal in Perth just after midday Tuesday after fly-in, fly-out workers arriving in Perth from Cloudbreak airport in the Pilbara had inadvertently walked into the secure passenger area without going through standard security screening.

For everyone's safety and security, the passengers who had gone through the screening were asked to leave the terminal and go through the screening again with the new arrivals.

A Qantas spokeswoman told WA Today the passengers from the Cloudbreak flight had entered the terminal because they got off from the bus at the incorrect drop-off point.

"Passengers from QF1971 (Cloudbreak - Perth) entered the sterile area without having been screened," she said, adding, "Following the breach, all passengers in the terminal were re-screened."

The spokeswoman admitted there were a few minor delays as a result.

WA Today spoke to Sydney-based passenger Chris Peterson, who was in the Qantas lounge when the announcement for evacuation was made.

"It was a funny situation, everybody was hightailing it to join the line. Ironically those in the Qantas lounge were the last to join the queue. By the time we got (back to the line), there was a queue of 300 to 400 people, the line was snaking through the domestic terminal," he said.

Mr Peterson told WA Today he decided to leave and catch a taxi to Cottesloe beach for lunch since his flight was still several hours away.