No flights will be allowed into UK airspace from midday after an ash cloud from a volcanic eruption in Iceland moved into UK airspace, forcing the cancellation of all flights to Scotland and London airports.
Heathrow, which has 1,300 flights a day, and Stansted will suspend all flights from midday.
The Air Traffic Control Service (Nats), has imposed the restrictions after the Met Office warned ash could damage engines.
A BAA spokesman said: "Due to airspace restrictions, in accordance with international regulations as a result of the on-going volcanic activity in Iceland, we anticipate that all flights in and out of Heathrow and Stansted airports will be suspended from 1200 today.
"Therefore, we strongly advise passengers intending to fly from this time not to travel to the airport today.
Aerial footage dozens of planes all parked up at the terminals.
Budget airline Ryanair said it would not be operating any flights from the UK for the rest of the day.
Manchester Airport officials said: "These severe restrictions will cause disruption to all flights to and from Manchester Airport between 0700 and 1300 today.
"Other UK airports are also affected by the airspace restrictions and all passengers are advised to check with their airline before travelling to the airport this morning.
"We would like to apologise to passengers travelling today for the inconvenience that this will cause."
Birmingham airport has warned of severe disruption with around 90 per cent of all flights cancelled.
East Midlands, Belfast City, Leeds Bradford, Cardiff and Southampton have also been hit.
A number of airlines have issued advice too. A spokesman for easyJet said:"EasyJet passengers are advised to check the website before they leave for the airport for any disruption information."
The plume of volcanic ash comes from an eruption under a glacier in the Eyjafjallajoekull area of Iceland. The volcano erupted on March 20 after almost 200 years of silence.
"It could be a threat in these areas from now until tomorrow or Friday."
The National Air Traffic Service 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."
Hundreds of people in Iceland were evacuated from their homes yesterday, amid fears of a second volcanic eruption.
Rognvaldur Olafsson, a chief inspector for the Icelandic agency, said some 800 people near the Eyjafjallajokull volcano were evacuated after reports of seismic activity suggested it may have erupted for the second time.