Many planes have been grounded at Heathrow
BAA advice
Armed police are patrolling terminals and travellers are undergoing searches.
Heathrow airport has been the worst affected, although the ban on short-haul flights into the airport was lifted on Thursday afternoon.
Speaking at Heathrow, Tony Douglas, from airport operator BAA, said it would be "open as usual" on Friday.
"It's been open all day today and it will continue to be open tomorrow and going forward," he told BBC News on Thursday night.
New security restrictions would remain in place, he added.
"The message for passengers is very clear.
"Don't bring carry on luggage and don't bring personal belongings unless they fit the list that's been provided and presented in a clear plastic bag.
"And please, most importantly, check with your airline that their schedule's being operated tomorrow or over the weekend before you come to the airport.
"Finally, allow enough time for the new security processes."
All cabin baggage must be processed as hold baggage and carried in the hold of passenger aircraft departing UK airports
Advice to passengers
At a glance: disruption New luggage guidelines Send us your experiences
A Department for Transport spokeswoman said the government hoped the current hand baggage restriction would be in place only for a "limited time".
The measures were "proportionate to the threat now" and would continue "only as long as the situation demands", she added.
Earlier, sources close to Transport Secretary Douglas Alexander indicated restrictions could become permanent.
One source told the BBC the "way we travel will never be the same again".
Mr Alexander will chair a meeting of the National Aviation Security Committee on Friday afternoon to consider security measures at airports and on planes.
Thousands disappointed
Despite Thursday's disruption, many passengers have praised airlines for keeping them informed and said they understood why the measures had been introduced.
Security has been increased at Channel ports and the Eurotunnel terminal.
Eurostar said it had taken at least 5,500 extra passengers to European destinations from London Waterloo on Thursday as a result of "displaced airline passengers".
This was 24% up on normal business, a spokesman said.
British Airways cancelled more than 360 flights at Heathrow by mid-afternoon, while easyJet and Ryanair also had to disappoint thousands of travellers by cancelling flights.
Many holidays have been ruined by the delays
The BBC News website's Krishan Rama at Heathrow said travellers were not as worried by the security operation as by the inconvenience of being allowed to take just passports and medicines on the plane.
Courteney Dane, who is travelling back to Australia, said: "I'm worried about the cost and the fact I've got a 24 hour flight with nothing to read. I'm not really worried about the security, it's just a nuisance."
Charlotte Demant, a make-up artist, has been in Ghana for two weeks and was on her way home to Denmark.
She said: "I can understand why they are worried about security but the airline has not been helpful.
"We should have at least been given something to eat and drink and money to phone home. I'm going to end up spending the night here in the cold airport."
By late afternoon, queues continued to build around terminal four as passengers packed into the building.
Armed police have been drafted in to many airports. Sussex police said extra officers were on duty, adding: "We appreciate that there is major disruption at and around Gatwick airport today but please be assured that we are responding to a very serious risk and that the action being taken is absolutely necessary to minimise that risk."
Increased security
Scotland's airports were busy throughout the day but passengers are still being advised to turn up even though there may be long queues for check-in.
All hand baggage will now have to be checked in with only a small number of essential items allowed through search controls
Douglas Alexander
West Midlands disruption Hold-ups at Stansted Disruption at Gatwick
Commentator Murray Walker was one of those stuck at Aberdeen. "I was supposed to be flying to Heathrow and am hoping to transfer to Birmingham, I have got to get to Silverstone.
"It's better safe than sorry, but I have a problem with those who are making this happen."
Felix Eza, from Failsworth in Manchester, was philosophical about the delay to his journey from Manchester to Orlando, Florida.
"If they [the terrorists] achieve their objective to disrupt our lives then it's a problem because they have won," he said.
Passengers are being asked to be patient when facing delays
Announcing the security measures on Thursday morning, Mr Alexander outlined the steps passengers needed to take.
"What these changes mean in practice is that all hand baggage will now have to be checked in with only a small number of essential items allowed through search controls," he said.
"Exceptions will be in place for those travelling with infants and for prescription medicines."
Passengers are being asked to check in most items of baggage, apart from wallets and purses, identity and travel documents, prescription medicines, spectacles and sunglasses and keys.
Those travelling with children will be allowed items essential for caring for them on the flight.
New Scotland Yard


La seccional antiterrorista y el servicio de seguridad de la Policía Metropolitana de Londres han afirmado la mañana del jueves (10) haber conjurado un plan terrorista para detonar bombas en al menos diez aviones en pleno vuelo desde el Reino Unido hacia los Estados Unidos. Las bombas iban a ser llevadas a bordo ocultas en equipaje de mano.

La operación antiterrorista se realizó durante varios meses. Scotland Yard afirmó que ha arrestado a 21 personas en Londres, Birmingham y el Valle del Támesis. En una rueda de prensa la tarde del jueves (10), el ministro del Interior John Reid declaró que la policía cree que los detenidos eran los "principales actores" del complot y afirmó que ''"de haberse concretado el plan la cantidad de víctimas habría sido de una dimensión sin precedentes"''.

Por su parte, Paul Stephenson, Comisionado Adjunto de la Policía Metropolitana (es decir, el "número dos" de Scotland Yard), dijo que ''"estamos convencidos de haber frustrado un plan elaborado por terroristas para causar un número de muertes y destrucción incalculables. Dicho simplemente, pretendía ser un asesinato masivo a una escala inimaginable"''.

Peter Neumann, analista del London's King's College, le dijo a la agencia Reuters que ''"este tipo de ataques con explosivos líquidos es especialmente preocupante. Los aviones siguen siendo vulnerables y en las próximas semanas los terroristas estarán pensando en algo más que hacer sobre lo que no tenemos ninguna idea. Si esto hubiese resultado habría sido, más allá de toda duda, el mayor complot terrorista en el Reino Unido"''.

''"En los últimos dos meses al Qaida prometió que vengaría a Iraq y Afganistán atacando activos aeronaúticos británicos y estadounidenses. Yo veo un lazo directo con esto"'', señaló el experto en terrorismo Paul Beaver.