Eurostar and Eurotunnel services through the Channel Tunnel have been suspended because of a power fault.
The blockage has left passengers in London and Paris stranded while they wait for it to be resolved.
Romain Dufour of Eurotunnel, which operates the tunnel, said technicians are examining what caused the electrical outage and are working to fix the issue.
Eurotunnel said: "Our passenger service is temporarily suspended due to a technical fault in the tunnel which is in the process of being resolved.
"We sincerely apologise for the inconvenience this will cause to your journey."
The fault began around 2pm and the company said it estimated services will not resume before 5pm.
Customers have been offered transfers to Dover and then onward travel to Calais by ferry.
One passenger wrote: "On train in Gare du Nord with delay - can someone turn the blasting air con off? Uncomfortable enough without being frozen into seats!"
Another Twitter user said: "Are you aware yet of the estimated time of departure? My husband has serious mobility issues and it's unbearable in here Lille!"
Some passengers sent messages to Eurostar via social media to express their frustration.
Additional reporting by PA
