A security breach at the Qantas domestic terminal in the Melbourne Airport has prompted the evacuation of passengers this morning causing some delays for thousands of passengers.

To avoid any unwanted incidents, the domestic airport had to be evacuated and screened everyone inside again, a spokesman for Qantas Thomas Woodward said in a report and quoted by the Sydney Morning Herald.

The CCTV camera in the airport showed a person, believed to be a man, entered the "sterile" area of the terminal at about 9:30am today via the exit doors from the baggage collection area

"When you get off a flight and exit at the arrivals hall to collect bags, there are three doors, which you go through," said Qantas spokesman Thomas Woodward. "A passenger has evidently, for whatever reason, gone through one of those doors and obviously hasn't been security screened at all, so unfortunately we're having to bring everyone back out from the secure areas for rescreening."

He noted that although they have spotted the man who breached the security they lost track of him while inside.

Thousands of people are now being cleared out of the terminal to be rescreened by security.

Mr Woodward said the process of re-screening all the people in the airport numbering close to 6,000 will take more than hour to complete.

Qantas would need to tighten security in both entrance and exit terminals to avoid this similarly chaotic situation.