The only passenger rail link between Britain and the rest of Europe has been shut down indefinitely, Eurostar said, promising more travel misery for thousands of stranded passengers just before Christmas.

A Eurostar statement said the fleet was undergoing upgrades and that more tests were planned for Monday. But a spokeswoman said she could not guarantee that service would resume on Tuesday.

A statement posted to the company’s Web site urged passengers to delay their trips or seek refunds.

Services have been suspended since late Friday, when a series of glitches stranded five trains inside the Channel Tunnel and trapped more than 2,000 passengers for hours in stuffy and claustrophobic conditions. More than 55,000 passengers overall have been affected.

Some panicked passengers stayed underground for more than 15 hours without food or water, or any clear idea of what was going on prompting outrage from travellers and a promise from Eurostar that no passenger train would enter the tunnel until the issue had been identified and fixed.

Eurostar runs services between England, France and Belgium. The company said on Sunday that it had traced the problem to “acute weather conditions in northern France,” which has seen its worst winter weather in years.

Eurostar commercial director Nick Mercer said three test trains sent through the Channel Tunnel on Sunday ran successfully, but that it became clear that the especially bad weather meant that snow was being sucked into the trains in a way “that has never happened before.”

“The engineers on board have recommended strongly that, in light of further snowfalls that are happening tonight, we make some modifications to the trains on snow shields to stop snow being ingested into the power car,” he told the BBC.

The stoppage has already meant that about 31,000 people in Britain, France and Belgium have had to cancel trips on Saturday, and 26,000 more were expected to be affected Sunday. With a huge backlog of passengers still building, Eurostar is blocking any sales until after Christmas and Eurostar chief executive Richard Brown has warned that services may not be back to normal for days.

For those seeking alternative routes between Paris, Brussels and London, the winter weather was dealing out more bad news.

Nearly half of all flights out of Paris’ Charles de Gaulle and Orly airports were cut on Sunday through mid—afternoon, with more cancellations forecast for Monday. Belgium was also badly hit, with passengers in Brussels lining up for hours in an effort to rebook flights.

Tourist Paul Dunn, 46, who was stuck in Paris, said he was looking for alternatives but that information was hard to come by.

“We said: ‘Can we get the train to (the French city of) Calais and the ferry?’ They are saying: ‘We don’t know what you can do. You can try.”’

It is a measure of the popularity of the 15-year-old Eurostar service which whisks passengers from London to Paris or Brussels in about two hours that its closure has dominated news in Britain.

European parliamentarians on both sides of the Channel have criticized the train company as being irresponsible, while Britain’s opposition Conservative Party said the issue was a matter of “huge concern.”

Mr. Brown seemed to acknowledge that there were some problems, apologizing for the Friday’s incident and the ensuing delays, but defended his staff.

“I’m not pretending it went well. I think it went quite a bit better than people say,” he told the BBC.

The problems and passengers’ complaints about their treatment while trapped on board could deal Eurostar “huge reputation damage,” said Nigel Harris, the managing editor of Rail magazine.

“They have promoted themselves as the ‘green,’ stress-free alternative to flying and now they face a major technical issue that they need to get on top of,” he said.

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