Eurocontrol traffic flow information shows that the Icelandic volcanic ash cloud is affecting airspace in 12 European countries, forcing airlines to cancel hundreds more services today.
The organisation expects 11,000 flights in European airspace today compared with 28,000 on a normal day. Eurocontrol says there were 20,300 flights on 15 April.
Some 100-120 transatlantic flights, out of a regular 300, have arrived in Europe today.
Forecasts suggest that the cloud of volcanic ash is continuing to move east and southeast, says Eurocontrol, adding that the impact will continue "for at least the next 24 hours".
Latest data shows 20 specific airspace zones - including Norway, Sweden, Finland, the UK, Ireland, the Benelux, and sections of Germany and France - as 'zero-rated', with the result that all airports within them are unavailable.
"No instrument flight rules clearances will be issued that penetrate contaminated airspace," Eurocontrol's Central Flow Management Unit says.
Eurocontrol lists several airports in France as being zero-rated, including Paris Charles de Gaulle and Paris Orly, while other major airports in Germany and Poland are also unavailable as a result of the surrounding airspace closures.
These include Frankfurt, Berlin Tegel and Schonefeld, Hamburg, Cologne/Bonn, Dusseldorf, Leipzig and Warsaw.
But some flights between Norway and Sweden will be permitted to operate by local flow-management stations.
Sweden is to consider opening northern sectors while services in Northern Ireland and western Scotland, from the two Glasgow airports, may also be permitted today, along with North Atlantic traffic from Glasgow and Belfast.
Eruption of the Eyjafjallajokul volcano in southwest Iceland, and the resulting high-altitude ash plume, has led to the severe disruption. Eurocontrol warns that the eruption is reported to have intensified.