"There were two broken power cables, which is extremely unusual," a Eurostar spokesperson said, adding that they were separated by only a few kilometres,
Two Eurostar trains that had come from London were stuck outside Lille overnight before being towed to Lille where passengers were given places in replacement trains to Paris and Brussels.
Six other trains were delayed.
Passengers travelling to Brussels spent about eight hours stranded on the train with no electricity and arrived at 6.00am in the Belgian capital, while passengers from London reached Paris Gare du Nord at 3.30am.
All passengers will have their fare reimbursed and will receive free tickets for their next trip, Eurostar said on Friday.