All non-emergency flights in and out of the UK will be grounded until at least 1pm on Friday due to a cloud of volcanic ash.
Air traffic control company Nats said it would give further details later as to what arrangements would be in place on Friday.
The decision to close all controlled airspace in Britain has wrecked the travel plans of thousands of passengers.
Some services were able to land and take off early today before Nats, working closely with weather forecasters, took the step to ground all flights as ash from Iceland's Mount Eyjafjalljokull volcano arrived in British airspace on north-westerly winds.
Danish airspace is also shut and no aircraft are operating in northern Sweden or northern Finland.
Weather forecasters predicted that the ash, high in the sky and difficult to detect, could spread to France and southern Europe after crossing the UK.