CALAIS, France — The undersea train tunnel that has revolutionized travel between France and England can reopen and traffic should resume ‘‘progressively,’’ the operator said late Friday, after firefighters extinguished an intense blaze earlier in the day.
    Eurotunnel, which operates the tunnel, said technical checks confirmed one of the two tunnels was ready to be reopened, with cargo trains and shuttles for trucks starting again perhaps as soon as overnight.
    Eurostar, which operates sleek high-speed passenger trains through the tunnel, said it would not resume services before Saturday at the earliest.
    Firefighters endured extreme temperatures and cramped quarters as they put out the blaze.
    The fire deep under the English Channel left the British Isles cut off for more than a day from continental Europe other than by sea or air — the only routes that existed before the undersea tunnel opened to passengers in 1994.
    Laboring through the night Thursday, firefighters painstakingly worked toward each other from separate ends in France and Britain to combat the blaze, which broke out Thursday afternoon aboard one of the trains that whiz back and forth through the 30-mile tunnel, transporting trucks and holidaymakers’ cars.
    Firefighters spent no more than 15 minutes at a time inside the tunnel, because of the intense temperatures of up to around 1,832 F. The blaze was declared extinguished around midday Friday.
    Five of 14 people injured remained in hospitals Friday, said prosecutor Gerald Lesigne, who was investigating the blaze. Officials said some people had inhaled large quantities of smoke; others hurt their hands by breaking the train’s windows to escape.
    Officials appeared to rule out terrorism as a cause of the blaze, one of the most serious incidents in the history of the tunnel that has made day trips between Paris and London possible by high-speed train.
    French Transportation Minister Dominique Bussereau said the fire ‘‘likely resembles something accidental,’’ without elaborating. Eurotunnel CEO Jacques Gounon said he had no reason to believe the fire could have been ‘‘criminal.’’
    The Channel Tunnel is actually three tunnels, each 130 feet beneath the sea bed. One tunnel carries passengers and freight from France to England, while another runs in the opposite direction. They are connected to a central service tunnel, used for maintenance and emergency access.
    The fire was in the tunnel that runs from England to France. The tunnel has had a few fires in the past, including one in 1996 that shut freight traffic for months.
    Passenger frustrations in both France and Britain over the temporary loss of the tunnel showed how reliant people have become on the link. Some 26,000 people travel through it on average each day.
    The huge lines of trucks that built up on the English side lessened Friday as police told motorists to avoid the area. Police turned parts of a major highway into a giant parking lot for trucks, in an emergency procedure they dubbed ‘‘Operation Stack.’’
    Victoria Morgan was among the British tourists stuck at Paris’ Gare du Nord. She went to the station twice only to be told there were still no trains. It was time to fall back on the form of transport favored before the tunnel existed — a ferry to England from Calais in northern France.
    ‘‘You can jump up and down and scream and shout but it’s an accident, it couldn’t be helped,’’ said John Piears, 65, who was at the other end — at St. Pancras station in London — his trip to Germany and Austria with his wife in hiatus.
    ‘‘We’re on holiday and it’s all part of the fun. We’re going to have a coffee now and people-watch,’’ he said.
    The 30-car shuttle train was carrying 32 people — mostly truck drivers accompanying their vehicles — when the fire erupted about seven miles from the French side.
    ‘‘Suddenly we heard an explosion. We went to the back and we saw flames through the window, and we immediately felt the heat,’’ Polish truck driver Andrzej Czapla said.
    He said he and another driver forced open the doors and went into the tunnel.
    A truck driver identified as Patrick Lejein on French TV said: ‘‘The train chief was in a corner, panicking. We drivers broke the windows to get out of the train.’’
    Eurotunnel’s Gounon said people suffered smoke inhalation injuries because they evacuated the train themselves before tunnel operators had ventilated away the smoke, as safety procedures call for.
    While a popular success, the tunnel has flirted with financial disaster. Eurotunnel was heavily burdened by debt before reaching a restructuring deal last year. It assured investors Friday that any financial impact of the accident ‘‘will be limited.’’
    Eurotunnel shares closed down 0.56 of a percentage point, at euro8.96 ($12.60), in Paris trading.
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    Associated Press writers Jill Lawless in London, and Septime Meunier and Angela Charlton in Paris contributed to this report.