Some 25 flights have been delayed at Edinburgh Airport after police said they had foiled a plot to blow up several flights from the UK.
Passengers wait for news about flight times and cancellations
Hundreds of passengers using the capital's busy gateway experienced disruption after security was tightened on Thursday.
Strict restrictions were put in place, with travellers told that hand luggage would not be allowed on flights.
There was an increased police presence and passengers' shoes were checked.
Extra security measures were put in place at airports across the UK, including those north of the border, on Thursday.
Passengers complained of "bedlam" when they arrived at Edinburgh Airport on Thursday morning.
Some said they were unable to push in through the terminal's doors because of the crowds while others said they "had never seen anything like it".
Passengers were allowed to take passports on board flights
Many passengers decided to leave the airport and try again on Friday in a bid to avoid waiting in queues.
The alert came during the airport's busy holiday time, when Edinburgh sees about 20,000 passengers departing and 20,000 arriving each day.
Richard Jeffrey, managing director of Edinburgh Airport, said: "We are making sure passengers have what they need so we have increased the catering land-side and called in extra staff.
"On the whole most passengers have been very understanding. Security issues arise from time to time and people know this. It is an inconvenience for everybody.
"I have been told this is a 72-hour security alert but my thoughts are this could change.
"There have been delays and disruption to the operation so I would advise passengers to check with their airline to find out what delays there are to their flights."
He added: "We had information from the Department of Transport this morning to say passengers were not allowed any hand luggage on flights. They are only allowed wallets, purses and essential medical supplies. Everything else must be checked in."
The passengers affected at Edinburgh included Neil Anderson, 46, a sales manager from Oregon in North America, who was at the airport with his wife Kathy, 48, and children, Craig, 14, and 16-year-old Kerri.
They decided to postpone their trip to Paris following the security alert.
Mr Anderson, said: "We were planning to go to Paris for five days during our holiday trip to Europe but we are abandoning these plans now and will try again tomorrow.
"The kids are very upset but safety is paramount so we understand that it's just a sign of the times."