Airline passengers are facing massive disruption across the UK after an ash cloud from a volcanic eruption in Iceland grounded planes.
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.
The restrictions were imposed after the Met Office warned the ash was sufficient to clog engines.
Passengers were also affected in Norway, Sweden, Finland and Denmark.
Passengers were advised to contact their carriers prior to travel.
Experts have warned that the tiny particles of rock, glass and sand contained in the ash cloud would be sufficient to jam aircraft engines.
These are some of the main knock-on effects:
- Aberdeen, Edinburgh and Glasgow airports shut
- Disruptions to and from Liverpool's John Lennon, Manchester and Newcastle airports
- Severe delays at Birmingham airport with problems reported at East Midlands, Leeds Bradford, Cardiff International and Bristol airports
- London's Gatwick, Heathrow and City airports hit
- British Airways cancels all domestic flights on Thursday and offers refunds or an option to rebook
- Flights suspended at Belfast International Airport and George Best Belfast City Airport
- RAF Sea King helicopter flies a critically ill patient from Scotland to London
- Ash threat forces Great North Air Ambulance to be grounded
One passenger at Glasgow told the BBC: "I'm meant to be going to Lanzarote. We've travelled from Oban, leaving at 3am. Now we've decided we might as well just go home and do a bit of gardening."
Others switched form plane to train, with the East Coast line extending its 1830BST London to Newcastle service through to Edinburgh.
Budget airline Ryanair said no flights were operating to or from the UK on Thursday and it expected cancellations and delays on Friday.
A Nats spokesman said: "The Volcanic Ash Advisory Centre has issued a forecast that the ash cloud from the volcanic eruption in Iceland will track over Europe tonight.
"Nats is working with Eurocontrol and our colleagues in Europe's other air navigation service providers to take the appropriate action to ensure safety in accordance with international aviation policy."
The European air safety body, Eurocontrol, said the cloud of ash had reached 55,000ft and was expected to move through northern UK and Scotland.
Brian Flynn, assistant head of operations of its central flow management unit, told the BBC: "As it moves toward the Netherlands and Belgium it will dissipate and lose intensity, like any weather phenomenon. But we don't know what the extent of it will be."
Met Office forecaster Philip Avery said the ash could take several days to clear.
He said: "It is showing up on imagery at the moment, extending down as far as the Faroes but it looks as though the wind will drag it a good deal further south.
"Nats has good cause to be very cautious about this because in about 1982 a British Airways jumbo had the unnerving experience of having all four engines shut down as it flew through a plume of volcanic ash."
There was a nearly identical incident on 15 December 1989 when KLM Flight 867, a B747-400 from Amsterdam to Anchorage, Alaska, flew into the plume of the erupting Mount Redoubt, causing all four engines to fail.
Once the flight cleared the ash cloud, the crew was able to restart each engine and then make a safe landing at Anchorage, but the aircraft was substantially damaged.
A BAA spokesman said: "Passengers intending to fly today are asked to contact their airline for further information."
The eruption under a glacier in the Eyjafjallajoekull area of Iceland is the second in the country in less than a month.