International flights out of Auckland Airport have returned to normal after planes were held up and 1000 passengers re-screened when security at the border was hit by a power problem.

Although it was thought just over 50 passengers were affected, about 1000 people were rescreened after a power failure in a metal detector.

It took about four hours to fix the detector and clear the backlog as passengers were stopped from leaving the country, some even taken off planes and made to go through security a second time.

Auckland Airport tweeted just before midnight security screening had returned to normal.

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First flights started leaving after 11pm.

An airport spokeswoman said while 53 passengers were affected, however, as a precaution all passengers, some 1000 people, were being rescreened, an airport spokeswoman said.

She confirmed a "power incident" had compromised the security procedure earlier this evening.

By 10pm the spokeswoman said flights had been prioritised based on overseas' airport curfews and connecting flights.

Where connections were tight, flights would be given priority for leaving, she said.

"We are processing passengers as quickly as we can."

She could not immediately say what the average delay time would be or how many passengers had been re-screened.

The first two flights scheduled to leave were NZ6 to LA and NZ8 to San Francisco, she said.

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An airport staff member, who asked to remain anonymous, said many workers were having to work overtime to help fix the problem.

He had been working 13 hours so far.

"Airline staff aren't being told anything more than passengers - that there was an issue with a ... and as a result all passengers have to be re-screened."

It wasn't clear whether passengers would get any compensation as the delays weren't the fault of any airline, he said.

A reader contacted the Herald to say the queues at the airport were huge.

"Everyone being very patient but some information would be useful," they said.

Tony Potter and his wife were supposed to leave for Los Angeles at 7.30pm tonight, but the latest they've heard from Air New Zealand is that their flight is now delayed until at least 10pm.

"They're not telling us anything and people were quite accepting of it to start with, but now they are increasingly getting rather antsy," he told the Herald.

"It's one hell of a mess here. The place is pretty chokka."

He said gate six, where he was waiting, was full of people and several crying children.

Potter said he expected to be waiting even longer than 10pm to take off due to the amount of people needing to be re-screened.

All exits have been blocked so people cannot leave the gate area, Potter said.

The food court had been evacuated and people had been told they weren't allowed to go back and get something to eat.

"People are getting quite antsy."

Aviation Security spokesman Mike Richards said 53 passengers had passed through security before it was discovered one metal detector wasn't working.

It wasn't clear exactly what had happened but was possible a cord had been disconnected, he said.

Security officers at the gate had found it curious that no triggers were being detected as people passed through and double checked the machine, which showed it had no power.

"Anybody that had been through has been rescreened. It's quite a big job," Richards said.

Aviation Security would be checking CCTV footage to try and figure out what had caused the problem.

"Our focus is always on safety and security and we couldn't allow anyone to go through who hadn't had that safety check."

The machine was now working again.

Auckland Airport's spokeswoman said all international flights would be held but could not say how many had been due to depart.

There would be flight delays but at this point it was unclear how long they would be, she said.

"There will be some delays which we do apologise for."