A power outage left Edinburgh Airport without lighting and affected the computer system and air bridges.
The power cut happened at around 9am, with the airport saying it was restored around 50 minutes later.
The cause of the outage is under investigation.
A statement from Edinburgh Airport said: “We can confirm that power is now returning to the terminal and that flights have resumed.
“We’re working to allow passengers to continue their journeys in a safe and ordered manner and we thank passengers for their patience whilst we do this.
“As always, the safety of passengers and staff is our priority.
“We expect there to be further delays whilst we clear the backlog.”
Following a ‘test call’, an announcement delivered an apology to all passengers for the loss of power, saying an ‘ongoing fault’ was to blame and airport staff were hoping to rectify the issue ‘shortly’.
Emergency lighting was in operation in some parts of the terminal but it is understood that the tannoy system was affected and as a result.
Passengers in the terminal reported long delays at security, while a video posted by one traveller shows the security hall in near-total darkness.
Other travellers queued outside the terminal as stewards directed people inside in groups.
Mike Hellier, 62, flying to Exeter for business, was among those waiting outside to get into the terminal.
He said: “I didn’t expect to come in and be in quite such a long queue.
“Because the tannoys aren’t working there was a lack of information [but] they seem to have done quite well.
“There were people coming up the line telling us what was happening so I’ve been pleased with the way they responded.”
Rachel Johnson, 43, was at the airport with her two children as they prepared to fly back to the United States.
She said: “We just turned up and found it. We didn’t check in online and hadn’t even gone online.
“They seem to be trying to keep us informed, walking up and down and letting everyone know about flights.
“We thought a bus had broken down at first. Everybody seems in fairly good spirits - nobody is trying to push in and be grumpy.”
Sheila Smart, 57, had to wait in a plane on the runway for about 45 minutes before passngers were able to get off.
She described the inside of the building as “absolute chaos”, adding: “They told us while we were in flight that there was a power cut so we had to circle for around 20 minutes before we could land.”
Toilets were also reported to be out of action ‘for safety reasons’.
Lothian Buses airport services were unable to access the airport and as a result were terminating at the DoubleTree by Hilton Hotel on Eastfield Road.
Gordon Robertson, director of communications at Edinburgh Airport, paid tribute to airport staff and spoke to thank passengers for their patience.
He said: “We train long and hard for situations like this and we have put those crisis plans into place this morning and I’m glad to say that they worked.
“The power was turned back on - we were less than an hour without power. Our focus has been getting power back to the terminal and helping our passengers get back on their journey which has been the focus for the entire team.
“It certainly has been a team effort. Everyone in the airport has been helping passengers and the passengers have responded really well, they have been really patient [and] understanding and we helping as many of them as we can get on their journey.
“We have a bit of a backlog and there will be delays for the rest of the morning, possibly some in the afternoon but we are working very hard to make sure we are getting the passengers through.
“Our priority this morning has been to get back up and running and to get passengers on route. However investigations are going on and that’ll be our focus for the rest of the day.”