London, England (CNN) -- Eurostar canceled all service this weekend after severe wintry weather in northern France caused the breakdown of an "unprecedented" six trains, stranding thousands of passengers on both sides of the English Channel on the weekend before Christmas.
Five trains with about 2,000 passengers stopped running Friday night inside the Channel Tunnel, also called the Chunnel, which runs between Britain and France. A sixth train broke down Saturday after Eurostar tried to run four trains from London to the Continental mainland in order to prepare for the resumption of normal service. About 700 people were aboard when that train stopped in the Ebbsfleet area of Kent.
In a statement on its Web site Saturday, Eurostar said it will conduct a series of test trains Sunday "to better understand the problems that have been occurring."
"We are committed to restoring our services as soon as possible but our key priority is the safety and comfort of our customers," the statement said.
Those passengers affected by the breakdowns are being offered a full refund, another return ticket, and 150 pounds in compensation. About 25,000 people should have been traveling on Saturday, Eurostar said.
"We strongly recommend that travelers whose journeys are not essential change their tickets for travel on a later date or have their tickets refunded," Eurostar said on its Web site.
The trains became stuck in the tunnel because the air inside was much warmer than the air outside the tunnel entrance in France, Eurostar spokeswoman Amelle Mouhaddib told CNN.
"It's a bit like taking a bottle of beer out of the fridge into a warm room -- within minutes it's covered in condensation," said Eurostar CEO Richard Brown. "We think that was the principle cause of the electrical failures on the trains."
He called the number of breakdowns "completely unprecedented."
Eurotunnel, which operates the Channel Tunnel, said it evacuated all 1,364 Eurostar passengers who were stuck Friday after the trains "lost traction," but one of the five trains remained in the tunnel and was blocking part of it, according to a Eurotunnel spokeswoman who asked not to be named, in keeping with policy.
The train that broke down Saturday was being towed back to the tunnel entry so passengers could be removed and transferred, Eurostar said.
Passengers evacuated Friday night described how a trip that was supposed to take around two hours lasted more than 14, factoring in the one-hour time difference between London and Paris.
"I left at 6:30 from Paris and we just arrived at 8 o'clock," passenger Robert Ricine told Sky News after arriving at London's St. Pancras station, a Eurostar hub.
He and other passengers complained they were given no food or water and little information during the ordeal.
"It was a very upsetting experience for those passengers traveling, and we're very sorry for what happened to them," Brown said. "We will be taking a very close look at what happened [and] what lessons can be learned principally to actually understand why it was that we had five trains breaking down."
The problems started after 9 p.m. (4 p.m. ET) Friday, when the first of the five Eurostar trains became stuck. It was helped out of the tunnel by a Eurotunnel locomotive, which took it all the way to London with passengers still on board, the Eurotunnel spokeswoman said.
Passengers on the second and third trains to fail were evacuated via the service tunnel to a Eurotunnel train, which brought them to the exit, she said. One of the failed trains was pulled out of the tunnel, but authorities were having difficulty removing the other, she said.
The fourth and fifth trains were running close together when they failed, so Eurotunnel locomotives coupled them and either pushed or pulled them to the English side of the tunnel, the spokeswoman said.
Passengers from the fifth train boarded the one in front, and Eurotunnel locomotives then towed that train to London, she said.
The Chunnel is actually two tunnels separated by a third and smaller service tunnel, so the train that remained stuck inside did not mean the entire tunnel was blocked, the Eurotunnel spokeswoman said.
The Chunnel is 50.5 kilometers (31.4 miles) long, 38 kilometers (23 miles) of which are underwater.
Brown said keeping passengers on the trains is the quickest and safest evacuation method.
"Because there were five trains, it took us ... longer than we would wish to get those trains out and those passengers on their way home," he said.
Despite the stoppage of service Saturday, noncommercial vehicles, including cars, motorbikes and camper vans, were still able to travel through the tunnel.
French authorities told all trucks to get off the highways on the French side of the Channel because of the hazardous conditions, Eurotunnel spokesman John Keefe told CNN. No trucks were entering the tunnel from the French side, and trucks were unable to enter on the English side because they wouldn't be allowed to drive upon reaching France.
The trouble resulted in a backup of freight traffic on either side of the tunnel, Keefe said.
On the British side, Kent Police early Saturday implemented Operation Stack, which goes into effect any time there is a problem affecting freight traffic in the tunnel. The operation lets police manage the backlog of trucks that builds up whenever the tunnel is closed.
A Kent Police spokesman could not estimate how many trucks were waiting Saturday morning but said Operation Stack allows police to manage as many as 2,300 trucks.
The poor weather in France also created problems for boats intending to sail across the Channel from England.
The Port of Dover, a major exit point to France, was operating restricted services Saturday because of weather problems in Calais, France, according to the port's Web site.
"The French authorities prohibited traffic from leaving the Port of Calais owing to the treacherous road conditions, which curtailed all services to Calais," the port said. "Tourist traffic is now being permitted to use the port and ships are sailing to Calais."
It was not immediately clear whether freight traffic had resumed between Dover and Calais.
CNN's Melissa Gray contributed to this report.