London, England (CNN) -- Rail and ferry services across Europe have been swamped by thousands of frustrated passengers forced to seek alternate modes of transport, as a volcanic ash cloud continues to disrupt European air travel.
The plumes resulted in the closure of some of the world's busiest airports, including Charles de Gaulle in Paris and London's Heathrow, as national aviation authorities closed airspace across much of Britain, Ireland, Sweden, Norway, Belgium, Denmark, Finland, Estonia, the Netherlands, France, Germany, and Poland.
"We've not seen anything like this before," said Rochelle Turner of Which? Holiday magazine. "It's been pretty devastating. We've seen television pictures of people stranded and airports empty. It's been difficult to provide them with advice because the picture keeps changing.
"However I'm pleased to see that many of the airlines are providing clear updates and information on their Web sites. But the best thing for people to do is to make alternative arrangements, such as rebooking your flight or seeking a refund."
Under European regulations, passengers whose flights have been cancelled must be given a choice between rerouting to their final destination or a full refund.
But the need to travel has forced many people to look at alternate modes of transport, which is putting strain on Europe's transport network.
Britain's air traffic authority, NATS, said airspace over much of the UK would be closed to all flights except emergencies at least until 1 a.m. Saturday (8 p.m. ET Friday), prompting many people to head for rail stations and ferry ports.
Eurostar, which provides Britain's only land link with Europe, urged people to stay away from its St. Pancras rail terminal in central London unless they held a confirmed reservation for travel. They reported a huge surge in demand for tickets.
Nicola Marinelli, from Mantiova in northern Italy, told CNN he arrived in London on Wednesday to watch some musicals and is now stuck. "I'm trying to get to Paris to get a train to Italy," he said.
Francis Kruyer, a London-based finance analyst, explained he was trying to buy a Eurostar ticket from Brussels to London for his boss, who is stuck in Frankfurt. "On the Web site the tickets were available," he said. "But when I put in my payment details it just went down."
P&O ferries, which operates many of the sea routes between Britain and Europe, said its Web site was struggling to cope with a huge increase in enquiries and urged customers to call its contact center with enquiries or to book a crossing on any route. It added that there was no space available on its busiest service between Dover in southern England and Calais in northern France.
Many travelers, however, had little option but to find hotel accommodation for the night, which is particularly difficult in London according to Visit London. A spokesperson for the city's official visitor organization told CNN that most hotels in the capital have an 80 percent occupancy rate at this time of year.
In addition to people trying to leave the UK, the continued disruption was likely to affect thousands of holidaymakers trying to return to Britain after the Easter break.
The Travel Association (ABTA), which represents hundreds of UK tour operators, told CNN that its members will be doing all they can to help passengers during this unprecedented crisis. But it said tour operators did not have a legal obligation to pay for extra accommodation for travelers stranded in holiday resorts.
Christian Cull of First Choice and Thomson Holidays told CNN that they are focused on helping people out in their resorts and customers at airports, while those who have booked holidays already that have been affected by cancellations will be offered alternative trips.
However, insurance cover is slightly more complicated, according to Rochelle Turner. She warned that travel insurance companies have been inconsistent with their advice to customers.
"It's difficult for many to know if they're covered," she said. "Some say you are, while other policies are calling it 'an act of God.' No-one has one clear policy so it's all about reading the small-print."
Republic of Ireland
Low-budget Irish carrier Ryanair said that based on current meteorological forecasts it expected fight cancellations to continue till at least 1300GMT Monday.
As a result, it said, it has decided to cancel all scheduled flights to and from the UK, Ireland, Denmark, Finland, Norway, Sweden, Belgium, Holland, Northern France, Northern Germany, Poland and the Baltic States until that time.
"This decision has been taken by Ryanair in order to allow passengers to apply for a full refund or rebook onto flights operating later next week," the statement continued, "when Ryanair hopes that improved weather conditions may allow normal flight services to resume."
Irish Ferries, which operates services between Ireland and the UK, said flight cancellations by carriers including Aer Lingus and Ryanair had a "huge impact" on business and that extra staff were brought in to deal with reservations.
According to the Irish Times, The Jonathan Swift sailings from Dublin to Holyhead on Friday were "sold to capacity," while a spokesman for Stena Line said it was "under siege," with one ship described as "packed to the gunwales."
Across the English Channel, a rail strike threatened to bring further chaos to an already busy weekend in France.
The strike by rail workers, in its tenth day, brought disruption to the high-speed TGV service, as well as regional trains in the south of the country.
"The roads will be very busy as thousands of school children from the Paris area are returning from their Easter break, while children from other regions start theirs," said CNN's Jim Bitterman.
More than 20 airports have been closed, while thousands of stranded passengers scrambled to find other options, such as renting cars and taking trains. France 24 reported that large crowds of disgruntled passengers converged on Paris's Gare du Nord station where Eurostar laid on three extra Paris-London trains.
At Warsaw's main train station, CNN's Frederik Pleitgen explained that people were queuing for up to four hours for tickets, but now most of Friday's services out of the the capital are fully booked.
One American family pored over a map as they surveyed their options for getting back to the United States. One option, the father explained, was to take a train to Vienna, Austria and then hopefully catch whatever flight was U.S.-bound.
"The second option is to take a ten-hour train journey to Frankfurt, via Berlin, then hope we can get a connection to America when we get there," he said.