Dozens of people were stranded for hours inside the Channel Tunnel after a train from Calais to Folkestone appeared to have broken down.
Images emerged showing Eurotunnel Le Shuttle passengers being evacuated through an emergency service tunnel after having to abandon their vehicles.
They were eventually transferred to a replacement train and taken to the Folkestone terminus in Kent.
A Eurotunnel spokesman said services had already returned to normal.
Le Shuttle said the incident on Tuesday night started when the train’s alarms were activated and that it needed to be investigated.
A spokesman said such incidents were unusual but not exceptional, much more common on truck-carrying trains than private cars.
“The Shuttle was brought to a controlled stop and inspected. As a precautionary measure, for their safety and comfort, we transferred the passengers on board to another shuttle via the service tunnel (which is there for exactly that purpose),” the spokesman said.
“We brought them to the passenger terminal building, where food and drinks were available, and then slowly brought out the original shuttle and reunited them with their vehicles.”
Sarah Fellows, 37, from Birmingham, told the PA news agency she found the service tunnel “terrifying”.
She added: “It was like a disaster movie. You were just walking into the abyss, not knowing what was happening. We all had to stay under the sea in this big queue.
“There was a woman crying in the tunnel, another woman having a panic attack travelling alone.”
Another passenger, who did not want to be named, said: “Several people were freaking out about being down in the service tunnel; it’s a bit of a weird place… We were stuck down there for at least five hours.”
All those on board the train were transferred at 20:22 BST (19:22 GMT) “in line with safety procedures and as a comfort measure”, Le Shuttle said.
A passenger contacted the BBC before 17:45, saying they were on the train, which had stopped. The passenger complained of poor communication, with the public address system not working correctly.
The service transports passengers and their vehicles between Folkestone and Calais.
At 37.9 kilometres (23.5 mi), it has the longest underwater section of any tunnel in the world.
There were about 100 vehicles on the halted shuttle. Le Shuttle said all passengers would be contacted individually to arrange compensation.