Eurostar has resumed some services after all trains from London towards Paris, Amsterdam and Brussels were cancelled due to a power outage in the Channel Tunnel.
Trains that have not been cancelled will be subject to "severe delays and possible last-minute cancellations" and passengers are advised to postpone their travel to a different date, Eurostar said.
The Channel Tunnel has partially reopened, and Eurotunnel LeShuttle services - which carries road vehicles and passengers through the tunnel between Folkestone and Calais - have also resumed.
The Department for Transport says disruption is "likely for the remainder of the day" while faulty overhead cables are repaired.
National Rail has advised passengers not to come to London St Pancras International if their Eurostar train is cancelled.
Eurostar's services resumed with the 15:04 train from London to Brussels departing after 16:00.
The 17:31 and 18:01 services to Paris will open an hour before departure. The 18:04 to Amsterdam is also showing on the board.
A broken down Le Shuttle train was also moved out of the Channel Tunnel.
On its website, Le Shuttle apologised and warned of delays at check-in and departures.
The LeShuttle service "resumed very gradually on one track" shortly before 15:00 local time (14:00 GMT), the EuroTunnel Press Office said.
"Service is operating alternately in both directions with significant delays," it said, adding that "additional shuttles will be added in the evening and until tomorrow morning".
Traffic has also eased on the M20 near the LeShuttle Terminal in Folkestone.
ReutersEurostar said the overhead power supply issue, which remains, started last night in parts of the Channel Tunnel.
The rail operator suspended services until further notice.
By midday on Tuesday, at least a dozen Eurostar services between the UK, France, Belgium and the Netherlands had been cancelled.
The rail operator apologised and said passengers could rearrange their plans free of charge or can cancel their booking and get a refund or an e-voucher.
Passengers told the BBC how the outage left them stranded and disrupted their holiday plans.
Ben Clark, from Bedfordshire, said he has been stuck on-board Le Shuttle in Calais with his wife and three daughters since 10:00 local time.
"The first two-and-a-half hours weren't too bad but the girls have got restless in the last half an hour so we've let them run around the boarding carriage to burn off some energy," he said.
"Some people are getting angry but there's nothing that can be done, others are sleeping in their cars. We have used up our snacks and now have no plan B or C."
ReutersOn the UK side at Folkestone, Matthew Webber, from Suffolk, said he has been stuck for hours and is unclear whether he and his group will be able to continue their journey.
"Not a lot of information being given out which is poor," he told the BBC.
"Lots of queues and everyone is waiting to get on the Tunnel. The conditions are very busy and people are leaving to get a ferry."
BBC / Nicky SchillerSteph Roberts, from Ashford, Kent, told the BBC she has been stuck at the Calais terminal with her husband Robert and bulldog Dempsey since 10:30.
She had spent two weeks in France seeing her parents and family over Christmas.
Ms Roberts said: "We've not had any updates or been given any food or water.
"We've just been spending the time going through social media and reading magazines. I've also gone out to take the dog for a couple of walks."
PA Media
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