By 5:00 am French time (0300 GMT), passengers on the 9055 train from Paris to London were still waiting at the Calais-Frethun station in northern France after "intruders" on the tracks blocked trains from entering the Channel Tunnel, a Eurostar official said.
Water and food have been distributed to passengers and "rescue services are also present for those who need help, particularly the elderly," added the official, describing the situation as "complicated".
A passenger aboard the train, Geraldine Guyon, said the situation remained tense in the station, which lies close to the port of Calais where some 3,000 migrants living in makeshift camps have been ramping up their attempts to cross the tunnel to Britain.
Clothilde, 23-year-old French woman who lives in London, said she had seen the police hurrying down the train and believed there were migrants on the roof.
Also Read
"We have not see the migrants, but we knew that they were everywhere on the roof and that's why we waited for a helicopter to ensure there were no migrants above us," she said, adding: "Passengers are not allowed to leave the station, except to take a taxi at the entrance."
"Once the train stopped, law enforcement intervened... and that blocked Eurostar services that were travelling towards London and the power had to be cut for safety reasons," he said.
A Eurostar official said the company hoped to transport passengers to London, the train's original destination, in the coming hours. Five other trains originally disrupted by the incident have either been sent back to where they departed from or on to their final destination.
"We are doing everything possible to ensure passengers are welcomed with a drink, food, taxis and hotels when they arrive," a Eurostar spokesman said.