Immigrants have also arrived as legitimate Eurostar passengers without proper entry papers.
Eurostar passengers at London's St Pancras Station are facing lengthy queues before boarding, with the company advising essential travel only.
Two British Eurostar passengers sparked a security alert in France after trying to board the high-speed train carrying a live artillery shell.
A Eurostar passenger stuck on a train for five hours during the series of breakdowns before Christmas is suing for "false imprisonment".
Arriving Eurostar passengers would leave the station by a new concourse at its north end.
Britain reluctantly accepted ending its insularity, but today 57 percent of Eurostar passengers are Britons, while only 26 percent are French.
Customs checks on Eurostar passengers remain unaffected by the agreements and continue to take place upon arrival after leaving the train.
They will be able to travel as passengers inside the sleek, new, high-speed Eurostar passenger trains that will depart several times each day to and from London, Paris and Brussels.
Eurostar passengers can exchange or refund their tickets.
Meanwhile, hundreds of Eurostar passengers were left stranded on trains, which had been halted outside the tunnel in both directions.