Eurostar, the high-speed passenger train that runs under the English Channel, halted service between Paris and London on Thursday because of “an unexpected strike” at the Channel Tunnel, leading to travel chaos ahead of Christmas.

As of Thursday afternoon, 25 trains scheduled to travel between London and Paris and between London and Brussels had been canceled, according to Eurostar’s website. Eurostar said on social media that trains would be unable to proceed through the Channel Tunnel until midafternoon on Thursday at the earliest.

“We’d urge all passengers to postpone their travel due to the Channel Tunnel closure and the continuing uncertainty,” a statement said. “Again; we are very sorry for the impact this is having.” Four trains were held mid-journey and would return to their starting points, Eurostar said.

LeShuttle, the train service that carries cars and trucks through the tunnel, was also suspended, according to a statement posted to its social media accounts, which blamed “French industrial action.”

Eurostar added that it did not yet have information about whether train services would continue as planned on Friday. On Thursday, only one train, at 9:10 p.m., was scheduled to depart from Paris to London. Two evening trains were scheduled to depart from London to Paris, according to the Eurostar website.

The Eurostar whisks passengers between Paris and London in about two hours and 15 minutes. It also runs between London, Brussels and Amsterdam, though the company said last month that its direct train service from Amsterdam to London would be suspended for six months next year.

Clement Beaune, France’s transport minister, said that blocking the Channel Tunnel was “unacceptable.” “A solution must be found immediately,” he wrote on social media. “I am calling upon on everyone to take their responsibilities, to ensure that traffic and holiday departures can continue under good conditions.”