Eurostar executives suspended service, blaming the breakdowns in the trains from Paris on wintry weather conditions on the French side of the English Channel.
Fatigued passengers arrived in London 10 hours late after a long night trapped on trains, where they said some people suffered panic attacks because of lack of air in dark, unheated cars short of water and supplies.
"They were useless at giving us information," said passenger Alison Sturgeon, who vowed never to take Eurostar again. "The conditions on that train were terrible. We slept on the floor on newspapers like hobos and nobody knew what was going on."
Her husband Steven Sturgeon said two off-duty London policemen helped people keep their spirits up, but that no Eurostar crew members provided help or guidance during the long hours they were trapped.
Embarrassed Eurostar executives apologized for the breakdowns and confusion.
"Eurostar is very, very sorry that so many passengers were inconvenienced last night and this morning due to weather conditions in northern France," chief executive Richard Brown said. "We are working hard to get passengers home; we will give them full refunds and another ticket."
Brown blamed the breakdowns on extremely low temperatures and heavy snow in northern France, which he called the worst in eight years. The problem began because of the abrupt temperature change when trains traveled through extremely cold air in France and then entered the warm tunnel, he said.
Eurostar said there were "extreme subzero" temperatures (in Centigrade) in northern France. The temperature inside the tunnels varies according to its depth but was much warmer than the air outside, it said.
Eurostar officials said all the passengers were safe and had been removed from the tunnel.
Two of the broken trains were pushed to London by smaller diesel trains. Television footage showed the modern, bullet-shaped Eurostar trains traveling slowly along high-speed lines as they were pushed by diesels.
Other passengers were evacuated on foot and put on Eurotunnel shuttles that brought them to nearby stations in England, where they were eventually put on regular trains bound for London or given bus transportation to the British capital.
When they arrived at St. Pancras International station in London, some passengers complained they were left trapped in trains all night long and then evacuated by firefighters who made them walk through the tunnel carrying their own baggage.
Some said the company failed to make arrangements for them even after they were safely evacuated and they spent hours at train stations in southern England waiting for transport to London.
Eurostar officials warned that service for the rest of the busy holiday weekend would be "severely disrupted" due to extreme weather conditions.
"We strongly recommend that travelers whose journey is not essential change their tickets for travel on a later date or have their tickets refunded," the company said in a statement posted on its Web site.
The company provides train service linking London to Paris and Brussels. It is usually thronged with holiday travelers this time of year.
The train service's reputation for safe operation suffered a setback in September, 2008, after a fire broke out as one of the trains entered the 50 kilometer (30 mile) tunnel. Service was cut back for five months as extensive damage was repaired.
On Saturday, travel for motorists hoping to cross the English Channel on ferries and via the Channel Tunnel was also badly disrupted. Police in Kent, England, warned drivers not to travel to the port of Dover except in emergencies because of massive traffic snarls caused by problems in the tunnel and in the French port of Calais.
Police put in motion a contingency plan to allow up to 2,300 trucks hoping to cross the English Channel to park on highways until the situation improves. Red Cross workers provided hot drinks and water to motorists trapped in their cars for up to 12 hours because of the traffic snarl.