All flights in and out of the UK have been suspended as ash from a volcanic eruption in Iceland moves south.More here:
Safety body Eurocontrol said up to 4,000 flights across northern Europe would be cancelled on Thursday.
The air traffic control service (Nats) said no flights would be allowed in or out of UK airspace until 1800BST amid fears of engine damage.
Norway, Sweden, Finland and Denmark were among the European countries hit.
Thousand of flights were canceled, stranding tens of thousands of passengers, and authorities said it was not clear when it would be safe enough to fly again.
One scientist in Iceland said the ejection of volcanic ash — and therefore possible disruptions in air travel — could continue for days or even weeks.
"It is likely that the production of ash will continue at a comparable level for some days or weeks. But where it disrupts travel, that depends on the weather," said Einar Kjartansson, a geophysicist at the Icelandic Meteorological Office. "It depends how the wind carries the ash"
In Paris, all flights north were canceled until midnight. At Copenhagen's international airport, spokesman Henrik Peter Joergensen said some 25,000 passengers were affected.