Liverpool Airport was not technically "evacuated", but passengers have been asked to leave the departure lounge after a technical problem with scanning machines.
The airport said passengers are currently being re-screened and there is no threat to passenger safety.
Large numbers of holidaymakers had to leave the main airport building after the glitch.
Manchester Evening News reported one passenger, Steph Hodson, said she was told the problem was a security incident to do with scanners.
"The staff all looked quite flustered and we could see everyone outside. There’s hundreds of people. I’ve spoken to a police officer and they said it’s an issue to do with the security scanners, and we were moved for our own safety," she said.
— Katie Mansfield (@katiemansfield_) May 20, 2016