"Airline traffic in parts of northern Europe is at a standstill because of ash spewing into the air from a volcano in Iceland. Hundreds of flights were cancelled Thursday morning as Europe's busiest terminal at Heathrow airport prepared to shut down. British airport operator BAA Ltd. said London's Heathrow and Stansted airports would close at midday Thursday and it was not immediately clear when flights could resume. ""We strongly advise passengers intending to fly from this time not to travel to the airport today. We will provide further updates as we get more information from air traffic provider NATS,"" the airport operators said in a statement on the Heathrow website. Gatwick, Britain's second-busiest airport, also planned to close. British authorities said no non-emergency flights will be allowed in any British airspace from noon."