Tens of thousands of airline passengers worldwide suffered long delays yesterday when stringent security measures on all flights to the United States went into force following the Christmas Day suicide bomb attempt.

Up to 25,000 passengers in Britain were held up for as long as three hours.

US-bound flights from Auckland departed on time despite the additional checks having to be introduced at short notice.

The US Transportation Security Administration imposed the new rules on all flights to America following an incident involving Nigerian Umar Farouk Abdulmutallab, 23, who allegedly tried to blow up a Northwest Airlines flight from Amsterdam to Detroit.

Yesterday, jittery authorities in the US had another scare. Armed officers rushed on board the same Amsterdam-to-Detroit Northwest Airlines service that was attacked on Christmas Day, but the cause of suspicion turned out to be an ill traveller who was too long in the bathroom.

At Auckland, the only airport from which Air New Zealand and Qantas operate direct flights between New Zealand and the US, staff were told of the changes on Sunday only six hours before the next scheduled flight to the US.

Aviation Security Service chief Mark Everitt said no aircraft were delayed.

He said about 30 additional staff had been helping to process passengers, who seemed to be heeding advice to allow an extra hour for checking in. "We have not had any complaints from passengers."

Between three and five flights leave Auckland for the US every day.

Mr Everitt said New Zealand's expertise in "balancing the use of technology and human resources" had helped.

"This looks like a step back into the 90s and we are in a very lucky position that our staff are well trained to apply the human factors rather than using technology."

He would not comment on the specifics of the new security checks, but they are understood to involve the use of sniffer dogs, rigorous luggage searches and body searches.

Mr Everitt described the additional security measures as "a stop-gap measure" and expected them to be reviewed and refined by the US authorities within the next five days.

Law enforcement leaders say Abdulmutallab claimed to have been acting on instructions from Al Qaeda to detonate an explosive device over US soil.

Investigators are trying to figure out how the device he had was made, how much of a broader threat it poses to air security and whether rules need to be further tightened.

Abdulmutallab had emerged from the toilet complaining of an upset stomach, put a blanket on his lap and allegedly tried to set off explosives strapped to his body. But passengers and crew overpowered him.

He has been charged with attempting to blow up the aircraft.

Passengers flying to the United States are now banned - in the final hour before landing there - from standing up, going to the toilet, opening lockers and covering themselves with blankets.

In-flight entertainment is also being withdrawn where the systems include flight maps showing the plane's location, for fear the bombers will use the information to pinpoint targets, the Times of London reported.

Air Canada and British Airways disclosed the security steps in notices on their websites.

"Among other things, during the final hour of flight, customers must remain seated, will not be allowed to access carry-on baggage or have personal belongings or other items on their laps," Air Canada's website read.

But New Zealand aviation commentator Peter Clark labelled the measures a "knee-jerk reaction" and an exercise by the American authorities in making people feel secure.

"It gives people a false sense of security, but does little or nothing at all for air security," Mr Clark said.

He said one of the ways to eliminate problems was to not allow any cabin baggage on board aircraft.

But even then, it was possible for people to carry on their bodies small amounts of chemicals or powders which existing screening methods were unable to pick up.

"Short of not allowing people to carry anything or wear any clothes on board an aircraft, there is no foolproof way of stopping this from happening in the future," Mr Clark said.

"The security in the United States is already extremely high now, and it seems to be that these people just go one step ahead against the security that's being imposed."

He said one way passengers could help to increase security was by being observant and monitoring the people they were travelling with and their surroundings.

They should report any suspicious actions.