Airlines across Europe cancelled flights bound for Heathrow Airport today, while some airports offered to take on diverted traffic after British authorities said they had thwarted a terror attack aimed at aircraft flying from Britain to the US.
Across the continent, travellers trying to get to Britain were stranded - and tempers were fraying.
"This is not fun at all. You get no compensation. Nobody gets any help here. You feel abandoned," said Cicero Alves Do Nascimento, a 47-year-old Brazilian martial arts teacher stuck at Amsterdam's Schiphol airport after his British Midland flight to Heathrow was cancelled.
The block on incoming traffic at Heathrow, Europe's busiest airport, applied to flights of three hours or less - effectively stopping most flights from Europe.
Heathrow flights were beset by massive delays, caused largely by emergency security regulations banning hand luggage. Authorities said the plot aimed to blow up several aircraft with explosives smuggled in hand luggage.
Laptop computers, mobile phones, iPods and remote controls were among items banned. Prescription medicines were permitted, as were eyeglasses but not their cases, the British Department of Transport said. Contact lenses could be taken aboard in their cases, but bottles of solution were banned.
British Airways said all its short-haul flights to and from Heathrow through 1400 GMT were cancelled. The airline advised passengers to avoid travelling if possible.
At Schiphol airport, KLM spokesman Hugo Baas said the airline had cancelled five flights to Heathrow.
"The backlog for people travelling to and through London is in the hours. That's going to create a ripple effect throughout the day, and increase as long as the airport remains closed," he said.
He said KLM was diverting to other London airports, and substituting larger planes where possible to increase the number of people reaching their destination.
Gabriele Pfeiffer, a lawyer for OEAMTC, Austria's largest advocacy group for travellers, cautioned people who had booked vacations in Britain to think twice before cancelling, or risk foregoing refunds.
"Vacationers should wait for further developments and under no circumstances hastily cancel," Pfeiffer said, citing court rulings that travel companies are not obligated to refund the cost of flight tickets or hotel deposits based on a terror warning alone.
"Whoever rushes into cancelling his journey to Great Britain now does so at his own risk," she said.
Alves Do Nascimento, the Brazilian traveller in Amsterdam, said he was rebooked on a flight for tomorrow but got no voucher for a hotel or food because the airline said it wasn't to blame.
The US government raised its threat assessment to the highest level for commercial flights from Britain to the United States and counterterrorism officials said flights operated by Continental, United and American were the likely targets of the foiled plot.
Frankfurt International airport, Europe's second-busiest, said it was prepared to take any flights diverted from Heathrow, but none had landed by mid-afternoon. The airport already has more than 1,400 planes landing and taking off daily, spokesman Wolfgang Schwalm said.
Schwalm said security measures had been increased but that no ban on hand luggage had been put into place at Frankfurt.
Austrian Airlines said a Heathrow-bound flight from Vienna was diverted to Brussels and that two other afternoon flights would be cancelled if Heathrow remained closed.
A nine-year-old girl at Warsaw's airport told Polish television that she was not sure if she would be able to get to London to see her mother.
"My mom is waiting for me there," the girl, who only gave her first name Klaudia told Poland's TVN24. "I am very worried because my mom does not know about that yet."
In Berlin, easyJet, British Airways, AirBerlin and Ryanair cancelled their London-bound flights.
Air France cancelled all morning flights to Heathrow because the airport was "saturated," an Air France spokeswoman said.
German carrier Lufthansa said its morning and early afternoon flights to Heathrow were cancelled. No other Lufthansa flights were affected.
All flights from Athens to airports in the London area were cancelled.. Spain's Iberia cancelled four flights to Heathrow, and Italian carrier Alitalia stopped six flights through London - four linking the city with Rome and two with Milan.
SAS, the flagship carrier for Sweden, Norway and Denmark, cancelled its flights to Heathrow from Stockholm, Copenhagen and Oslo. Irish national carrier Aer Lingus, which uses Heathrow as its only London airport, cancelled all flights to and from London in response to the alert.