Eurostar train services between Britain and Europe were suspended indefinitely Sunday due to the freezing weather, throwing the Christmas holiday plans of tens of thousands of people into chaos.

More than 24,000 people have already been affected, but the operator of the Channel Tunnel passenger trains said there would be no services for a third day Monday.

Eurostar sent test trains along the route on Sunday to see if they could withstand the freezing temperatures and snowy conditions in northwestern France which are being blamed for causing five trains to break down in the tunnel on Friday.

"Eurostar will not be operating services on Monday," the company said in a statement.

"We sincerely regret having to take this decision and we understand how frustrated and disappointed travellers will be, particularly those who have been waiting to travel for the last two days."

They advised passengers to switch their booking to a later date or claim a refund.

"We will provide a further update regarding Tuesday's services by 1800 GMT on Monday," the company added.

Eurostar's commercial director Nick Mercer said test trains had been running Sunday with engineers trying to work out what was making them break down.

They had made modifications to the trains, which will be tested Monday to ensure they are effective, he said.

Mercer said screens and shields meant to stop snow getting into the electrics had failed and needed to be improved.

"The test trains did run satisfactorily. The engineers believe they've found the cause," he told BBC television.

The weather conditions in northern France "caused snow to be ingested into the trains in a way that's never happened before," he said.

The big temperature change between the open air and the warm tunnels has also been blamed for the breakdowns.

"We're carrying our the modifications and I sincerely hope when we test those modifications in live service on these test trains, they will work satisfactorily and we'll be able to resume service."

More than 2,000 people spent Friday night trapped in the Channel Tunnel, some without anything to eat or drink, in stuffy conditions. Angry passengers have accused the company of handling the situation badly.

French Euro MP Dominique Baudis -- who along with his wife and son spent six hours trapped in the tunnel -- said he would demand an official inquiry into Eurostar's "failings".

"As a member of the European parliament, I plan to ask the transport commissioner to set up an inquiry into what happened," he told AFP from London, where he eventually arrived on Saturday.

"The chain of events was an aberration. Eurostar's complete inertia was scandalous," he said.

Eurostar made emergency arrangements for 500 of its "most vulnerable" passengers caught up in the chaos, taking them to the English port of Dover on buses before catching a ferry to France.

Passengers who have suffered delays will be offered a full refund of their ticket, a free return ticket, and 150 pounds (170 euros, 240 dollars) per person.

The Channel Tunnel runs for 50 kilometres (30 miles) between southeast England and northeast France. Opened in 1994, it is the world's longest uninterrupted undersea link.

Besides the Eurostar passenger trains, the tunnels also carry freight and vehicle shuttles.

Eurotunnel, which operates a cross-Channel drive-on train service for cars and trucks, said its services for cars were running on Sunday, but with delays.

The situation was worse for trucks, which were being held on the motorway leading to the Eurotunnel terminal in Folkestone, southeast England.

The problems with the Eurostar trains added to an already difficult situation for people travelling to and from Britain, where snow fell Sunday across northern England and western Scotland.

Passengers at Manchester Airport in northwest England experienced long delays while snow was cleared from runways, while airports in London and elsewhere in the country reported some cancellations and delayed flights.