They were moved from the departure lounge at the airport after a problem with a scanning machine earlier today.
A statement said: “Due to a technical problem with one of the airport’s passenger scanning machines, all passengers have been removed from the departure lounge and are currently in the process of being rescreened.
“There is no threat to passenger safety with this rescreening process necessary in order to ensure security compliance.”
An airport spokesman said passengers were back in the lounge by 1.30pm and it was business as usual, but there were some delays to flights.
A spokesman for Merseyside Police confirmed it was a “customer service issue” rather than a security alert.