“We invite travellers to postpone their trip,” it said in a statement.
Image: A view of a departures board at St Pancras station. Pic: PA
Trains to northern France have also been brought to a halt from Gare du Nord, which is a major European transport hub and considered the world’s busiest railway station outside of Japan.
Fridays are the busiest day of the week for Eurostar, as many holidaymakers embark on international weekend breaks.
French transport minister Philippe Tabarot said travel would be ”strongly disrupted” throughout the day with only limited service resuming in the afternoon.
Speaking on broadcaster Sud Radio, he said local residents and people near the train stations should have “no fear” of a risk of explosion, stressing the procedures in place for defusing and removing such bombs.
First and Second World War bombs are regularly discovered around France but very rarely in such a densely populated area.
Eurostar is giving passengers whose trains have been cancelled the option of either requesting a refund or voucher for the value of their booking, or to rebook for travel on an alternative service.
Trains between London and Brussels are unaffected.