Britain on Monday ordered a fleet of navy ships to rescue stranded air passengers as airlines stepped up an angry campaign to fly again in the volcanic cloud which has paralysed Europe's airspace for five days.
The huge ash cloud of kept up its regime of chaos over Europe, forcing the cancellation of another 20,000 flights, though experts said the eruption in Iceland was losing power.
Europe's three main airports in London, Paris and Frankfurt, remained giant ghost towns, ordered to stay closed until at least Tuesday. Some experts said severe disruptions could run several more days.
Britain ordered its navy flagship aircraft carrier HMS Ark Royal and HMS Ocean and HMS Albion to pick up thousands of marooned Britons and even troops trying to get back from Afghanistan.
Prime Minister Gordon Brown said he expected Ocean to be off the French coast - where many Britons have come from all over Europe - later Monday while Ark Royal was moving towards the Channel. HMS Albion was heading for northern Spain to pick up British troops returning from Afghanistan and some stranded civilians.
"This is the biggest challenge to our aviation transport network for many years," Brown said. He said consultations were being held about letting flights resume but stressed that the "safety of air passengers is of paramount importance."
Spain, one of the rare countries operating normally, said its airports would also be used to repatriate hundreds of thousands of stranded nationals from Britain, France and Germany who are stuck around the world.
The plan would allow carriers to bring extra flights to Spain as a first stage to getting passengers home. "We are going to give as many flight authorisations as Spain is capable of handling," Spain's Transport Minister Jose Blanco said.
As forecasters predicted the ash cloud could soon reach Canada, European transport ministers were to hold a video conference to work out how to get around the chaos sparked by Iceland's Eyjafjoell volcano.
"This is a European embarrassment and it's a European mess," said Giovanni Bisignani, director general of the International Air Transport Association as carriers reeled with hundreds of millions of dollars of new losses.
Authorities in Sweden, Romania, Croatia and the Czech Republic announced the resumption of flights. Switzerland and Denmark allowed jets to fly through their airspace but only above the cloud.
Finland's flag carrier Finnair said it would operate a flight from New York to the western Finnish city of Turku on Monday, when some Finnish air space was expected to be temporarily reopened.
Eurocontrol, a continent-wide aviation authority, said only 8,000-9,000 flights of the normal 28,000 would get into the air, and those mainly in southern Europe.
Nearly seven million passengers have been affected by the closures which governments say are essential for safety reasons.
Air France, British Airways, KLM and Lufthansa reported no problems after launching flights to test fears that the ash cloud would destroy jet engines.
"We are far enough in this crisis to express our dissatisfaction at how governments have managed the crisis," Bisignani told reporters in Paris.
"Risk assessment should be able to help us to reopen certain corridors, if not the entire airspace," he said, calling on aviation authorities to make decisions based "on real situations".
KLM chairman Peter Hartman reaffirmed a demand that "KLM will get authorisation as quickly as possible to restart a part of its operations and to get passengers to their destination."
Lufthansa's chief executive said that computer simulations from the Volcanic Ash Advisory Centre in London, on which the extension to the shutdown was based, "cannot be taken seriously."
"We have local knowledge, we have carried out test flights, and we are seeing that they do not correspond at all to what is being forecast out of England," Wolfgang Mayrhuber said on ZDF public television.
"No one wants to fly into a volcanic ash cloud but what we have seen in the last three days is completely different from something posing a danger."
The Association of European Airlines which brings together 36 major carriers called on governments for an "immediate reassessment" of the restrictions, saying they were having a "devastating impact".
"Airlines must be able to fly where it is safe to fly and make decisions accordingly," it said.
Winds have carried most of the ash spewing from Eyjafjoell across a wide swathe of Europe since last Wednesday.
But the eruption "diminished markedly" and the colum of ash is less than half its original height of 6,000 metres (19,500 feet) on Monday, Icelandic seismologist Bryndis Brandsdottir of the University of Iceland told AFP.