Ryanair boss Michael O'Leary tonight announced blanket weekend flight cancellations over safety fears for planes flying in northern Europe.
The budget carrier's chief said all services to and from the UK and Ireland and about a dozen other regions have been grounded until 1pm on Monday.
Mr O'Leary apologised to customers but said he was acting on advice that stable weather was continuing to push potentially dangerous volcanic ash over the region.
"This spreading cloud of volcanic ash is an unprecedented event in Ryanair's 26-year history, and we are continuing to work around the clock to minimise its effects on our schedules," he said.
Mr O'Leary insisted the airline would not take safety risks.
All Ryanair services in Denmark, Finland, Norway, Sweden, Belgium, Holland, northern France, northern Germany, Poland and the Baltic states have also been grounded.
Flights in central and southern continental Europe, which is largely unaffected by the ash cloud, are operating as normal.
Ryanair said it hoped the weekend no-fly order would give passengers a chance to seek refunds or rebook flights for a few days ahead, rather than book 24 hours in advance in the vain hope the ash cloud would dramatically shift.
"By which time we hope that either the prevailing winds will have changed direction or the ash cloud will have dispersed sufficiently to allow flights to operate safely," Mr O'Leary said.
Earlier it was announced that restrictions preventing flights in England and Wales to protect aircraft from the Icelandic volcanic ash cloud will remain in place until at least 7am tomorrow.
But air traffic control company Nats added that from 7pm today, restrictions will be lifted in a large part of Scottish airspace including Scottish airports, Shetland, Orkneys and also Northern Ireland.
Nats said this meant that some North Atlantic services could operate to and from these points and that there might be an opportunity for some flights to operate from the north into Newcastle after 1am tomorrow.
As far as transatlantic services are concerned, Nats warned: "Please note these arrangements do not mean that all flights will operate. Anyone hoping to travel today or tomorrow should contact their airline before going to the airport."
The company went on: "We are looking for opportunities when the ash cloud moves sufficient for us to enable some flights to operate under individual co-ordination with air traffic control.
"Some aircraft were able to operate at Manchester this morning, although restrictions are now reapplied to Manchester."
Describing the situation as "dynamic and subject to change", Nats added that it would review further Met Office information and make a further announcement about flights at 8.30pm today.
Nats said: "We continue to work closely with airports, airlines, and the rest of Europe to understand and mitigate the implications of the volcanic eruption."
This afternoon's statement at least provides some glimmer of hope for air passengers who have been largely grounded since noon yesterday following the eruption of Iceland's Mount Eyjaffjallajokull.
Earlier, some flights were able to run in the Republic of Ireland and in Scotland, although Transport Secretary Lord Adonis warned it was "likely that significant disruption to most UK air services will continue for at least the next 48 hours".
One of those caught up in the travel chaos was the Duchess of Cornwall. She had to cancel a visit to a Polish cultural centre in London, where she was to sign a book of condolence for the late President of Poland, Lech Kaczynski, because she was unable to fly from Scotland.
One airport able to operate today was Newquay in Cornwall, where flights to and from St Mary's Airport on the Isles of Scilly were running. These flights operate outside controlled air space so are not subject to the Nats restriction.
Prime Minister Gordon Brown apologised to travellers, saying he was sorry there had been so much inconvenience.
English airports were mostly deserted but small knots of passengers unaware of the blanket ban turned up to find empty check-in desks and no flights.
At Heathrow Airport today was student Hannah Miller, 21, from Sheffield, who was meant to be flying to Brisbane, Australia, to see friends she met while travelling last year.
She said: "We came down this morning as we'd been booked in a hotel overnight. But now we're here and we've got nowhere to go.
"Last night was stressful, but now we've just had to wake up and get on with it."
For the second day running, travellers unable to fly looked for alternative modes of transport.
Channel Tunnel high-speed train company Eurostar reported that its 58 services were full today.
This meant the company was able to handle more than 46,000 passengers on its trains running between London and Paris and Brussels.
Many people took to ferries to reach the Continent. P&O Ferries, whose routes include Dover-Calais, said it was unable to accept any further foot-passenger bookings before Monday "as a result of the unprecedented surge in demand due to the airline crisis".
Coach company Eurolines increased its services to Europe, while some hotels, including Warner Leisure Hotels, cut the cost of weekend breaks.
Holiday park operator Park Resorts said it had seen a 45% rise in inquiries since the air crisis began.
Robin Gisby, Network Rail's director of operations and customer services, said: "We are doing everything we can to help passengers whose journeys have been disrupted by the volcanic ash cloud.
"We have reviewed all engineering work we have planned for the next few days and, where it will allow train operators to run existing or extra services, this work has been cancelled. This mainly applies to long-distance operators on the East and West Coast Main Lines and on routes to the Channel ports."
Dr Ashley Steel, global chairman for transport and infrastructure at professional services company KPMG, said: "This is yet another dramatic and costly event for the global aviation industry which will have a significant impact on annual revenues of airlines in the UK and Europe.
"It will also affect airlines in the US and Asia because, in places around the world, airplanes bound for the UK and Europe have been grounded."
He went on: "Airlines will incur their biggest losses in the transatlantic business passenger category; the impact on economy class revenues is likely to be diluted because people will change their bookings and eventually still fly.
"However, the bottom line is, for an airline like BA every day of their fleet being grounded is likely to cost tens of millions of pounds.
"These unprecedented events underline again the need for mergers and global alliances in the airline industry because truly global airlines will be much better placed to deal with the financial fallout from these types of events."
Minicab company Addison Lee said it had received requests for journeys to cities as far away as Paris, Milan, Amsterdam and Zurich.
One booking, by a businessman, was to Salzburg in Austria.
Concierge and lifestyle management company WhiteConcierge said it had seen a huge increase in bookings for rail and ferry services.
The company added that its research revealed that, by 10.30am today, the average cost of a today-booked single train ticket from London to five major UK cities - Edinburgh, Cardiff, Leeds, Manchester and Glasgow - was 33% higher than those booked a week in advance.
Similarly, for ferry journeys from the UK to four ports in Europe - France, Holland, Dublin and the Isle of Man - the average price was 17% higher.
The organisation in charge of Europe's airspace is holding talks next Monday to review the airline crisis caused by the Icelandic volcano eruption, officials said this afternoon.
Eurocontrol, the Brussels-based European Organisation for the Safety of Air Navigation, signalled that it expected little change in the situation until then, as more countries closed down national airspace and the volcanic ash cloud continued its south-eastern sweep across the continent.
Eurocontrol deputy head of operations Brian Flynn said the incident had now become "major and unprecedented" with only 12,000 or 13,000 European flights operating today instead of the normal 29,500 anticipated.
He told a press conference: "We are effectively losing more than 50% of normal passenger flights."
He said the ash cloud was now being tracked at a height of 35,000ft (10,668m) over Europe.
Most of southern European airspace was operating normally, but for flights due to leave from or arrive at northern European airports, there was no movement - and none expected for some time.
Eurocontrol acts on behalf of 38 nations including almost all EU member states and the organisation has arranged talks on Monday to review the situation. The talks will take place via video conference because of the anticipated lack of available flights to get to Brussels early next week.
"Eurocontrol and the European Commission are taking the initiative with member states to harmonise and co-ordinate the management of this situation," said Mr Flynn.
"The tele-conference will look at measures which might be needed to mitigate the situation and allow airspace to be made available as soon as possible."
Joe Sultana, Eurocontrol's head of airspace, network planning and navigation, said: "There is significant disruption. The latest from Iceland is that sporadic volcanic eruptions are continuing so there is still ash being thrown into the sky.
"The wind patterns are pushing it south and sough east, and, coupled with high pressure over the Atlantic, no change is expected in the situation in the next 24 hours."
He went on: "This is a new situation for Europe. It is something we have rehearsed. We have simulated this volcano erupting and looked at the management of such a situation, but this is reality and we are working to mitigate the impact and ensure passenger safety.
"Our rehearsals have not covered something this big. We understand economic impact on airlines and the European economy, but safety comes first."
Eurocontrol says airspace is "currently not available for the operation of civilian aircraft in the UK,(except Scotland), Belgium, the Netherlands, Denmark, Sweden, Norway, Finland, Estonia, the north of France including all Paris airports, parts of Germany including Dusseldorf, Cologne, Hamburg, Berlin and the airspace around Frankfurt, and parts of Poland including Warsaw airport".
Neil Morris, senior manager in the aviation team at Deloitte, said: "We estimate that the cost to British and Irish scheduled airlines from the closure of British airspace is likely to be between £26 million and £28 million per day.
"After two days of airspace lockdown due to a volcanic ash cloud from Iceland currently floating above northern Europe, the estimated cost to the airlines so far is at least £52 million.
"Although some direct operational expenses such as fuel costs, landing charges and certain staff costs will not be incurred, they still have large fixed costs to meet such as operating lease rentals, paying staff and the loss of margin on ticket sales.
"The big concern is if there is further volcanic activity and the wind continues to blow in the direction of the UK.
"Following one of the worst years for financial performance the aviation industry has ever seen, a prolonged period of losses for an industry that is already in a difficult financial position could have serious repercussions."