National airport Management Company ANA confirmed reports that a “suspicious bag” led to the terminal being evacuated and a safety perimeter was set up around the area.
For over an hour hundreds of passengers were lined up outside in the street and authorities would not allow anyone to enter or exit the building.
Airport employees were stationed outside the terminal at Lisbon’s Humberto Delgado airport to control a confusion that had started to erupt.
The incident is understood to have happened at around 8.30am and things returned to normal less than an hour later.
Between those times the entrance to the terminal is said to have been blocked by police.