Air traffic in much of northern Europe was halted Thursday by ash from a volcanic eruption in Iceland, aviation authorities said.
"Due to ash, air traffic on the sea area between Scotland, Norway, northern Sweden, Britain, Norway and northern Finland is being limited," Finland's airport agency Finavia said.
A volcanic eruption in Iceland spewed black smoke and white steam into the air Wednesday.
Britain's National Air Traffic Service said that following advice from the Met Office weather service it had restricted the number of aircraft flying into British airspace.
"Volcanic ash represents a significant safety threat to aircraft," it said in a statement.
"We are monitoring the situation with the Met Office, Eurocontrol and neighboring countries, and working closely with the airlines to help inform their decisions about their operations."
Flights at London's Heathrow, Gatwick and other airports were canceled and there were no flights in or out of Scotland, with Aberdeen, Edinburgh and Glasgow airports all closed.
Belfast airport in Northern Ireland and Newcastle airport in the north of England also were shut.
British budget airline easyJet said the plume of ash, which is expected to move south, was causing "significant disruption" to all airlines operating flights to and from Britain.
Hundreds of flights in and out of other British airports, including Bristol, Cardiff, Manchester, East Midlands and London's Stansted and Luton were canceled, although the airports remained open.
Finnair said air traffic had been shut down in northern parts of Finland.
Norwegian news agency NTB said air space in northern Russia, parts of the United Kingdom and Denmark also could be affected.
National broadcaster NRK quoted an Avinor spokesman as saying it was considering closing down the remaining routes.
Norwegian Air Shuttle said it was cancelling some 80 flights, while SAS also halted many of its flights, according to Norway's main Oslo Airport.
It was unclear when traffic would resume. International flights south and east from the main Oslo airport were still not affected, agency NTB said.
HAVE YOUR SAY. Have you been affected by the flight disruptions? Write a comment below to share your story with us.