Eurostar customers have shared their experiences as they face delays of up to seven hours.
Those on board claimed they were stuck in poor conditions.
Holidaymakers were travelling from the UK to destinations including Brussels and Amsterdam.
Some used social media platform X to share their experiences today.
Customers took to social media to share their experiences
One claimed: "Trapped on Eurostar train for five hours at tunnel. No food, water, bathrooms or electricity. How is this acceptable?!
"No way to get to Amsterdam, travelling since 5am trying to get there! People are becoming ill and fainting."
Another added: "Been stuck on the Eurostar from London to Brussels for over five hours now there is s**t and p**s on the floor... I’m actually going mad."
A third shared what their experience had been. They wrote: "@EurostarUK we’ve been stuck on this broken down train for over two hours with no electric, no aircon, little updates and then when coming on here for answers we’re getting vague responses.
"We lost money on our trip and it looks like we’re not even going to Brussels! Awful!"
The Eurostar X account replied to this post urging travellers to look out for an announcement.
It said: "Understood; and we cannot but apologise to affected passengers onboard. "Announcements will now be being made without the address system. Please follow the direction of staff onboard. Thanks."
However, the social media user replied: "We’ve had announcements for over two hours and we’re still stuck on this train like caged animals and no idea if we’re going to our destination or back from where we left after wasting over two hours of our lives and having to pay for it!
"It’s awful! Everyone’s lost money and we just want to get off this train, it’s the worst travel experience I’ve ever had!"
Some claimed there had no bathrooms or electricity
The Eurostar X account shared more details in a post.
It said: "We're sorry for the delay to the #ES9114 today. The train is being detached from the overhead power lines but this is taking longer than expected."Due to a lack of power on board, it's not possible for announcements to be made. We apologise for the inconvenience."
It added: "We are aware of the very challenging situation on board 9114, and are extremely sorry for the experience. The train has now begun its way back to London.
"The situation was complicated due to the position of the train and the track infrastructure."
A spokesperson told GB News: "An overhead cable has fallen on the 08:16 Eurostar train, between London and Amsterdam, at the entrance of the Channel Tunnel. There are around 700 passengers and crew on board are confirmed to be safe.
"Following a complicated situation due to the position of the train and the track infrastructure, it’s meant that certain safety procedures had to be adhered to before we could move the train. The train is currently in the process of being brought back to London.
"All affected passengers on board will be met in London with refreshments and will receive enhanced compensation. Eurostar are sorry for issues caused that customers have experienced today."