Eurostar services have restarted on Sunday amid warnings of further delays and busy stations.

The first Eurostar train left London St Pancras International shortly after 8am.

“Unprecedented” flooding was brought under control on Saturday, meaning “at least one tunnel can now be used”.

But speed restrictions and uncertainty surrounding the second tunnel means further disruption is possible, the operator has warned.

Delays and cancellations are also expected on some domestic routes on Sunday thanks to staff shortages and bad weather.

At a thronging London St Pancras International on Saturday emotional travellers sat on suitcases, as people could be heard frantically trying to find alternative routes to their destinations.

A man, presumed to be a taxi driver, was also seen wandering around the station clutching an iPad which said “taxi to Paris”.

Britons were also left “stranded” in mainland Europe.

In a statement, Eurostar said: “Flooding in the Thames tunnels has been brought under control by Network Rail High Speed, meaning at least one tunnel can now be used and a full service can operate.

“There will be some speed restrictions in place in the morning which may lead to delays and stations are expected to be very busy.

“Unfortunately, this unprecedented event has caused major disruption to customers today.

“Customers are encouraged to visit the Eurostar website for more information on their journey and compensation entitlement.”

A spokesman for HS1, which runs the route between London and the Channel Tunnel, said: “Flooding in the Thames Tunnel is being resolved by Network Rail High Speed and the HS1 line will be operational in the morning.

“We understand how frustrating this has been for passengers and apologise for the inconvenience caused at such an important time of the year.”

The company has not revealed what initially caused the leak.

The problem began on Friday night when water filled tunnels near Ebbsfleet International in Kent, scuppering all high-speed services.

The spokesman said the cause of the flooding will be investigated, but added that there is no evidence to suggest it was caused by a burst pipe feeding the tunnel’s fire safety system as had previously been suggested by a water company.

Footage shot in the tunnel showed water gushing from a pipe and submerging the tracks.

Thames Water said it believed the flood was caused by a “fire control system and not a Thames Water pipe”.

Some railway tunnels, including the Channel Tunnel, have water systems installed as a fire safety measure.

On Saturday afternoon, engineers working in the tunnel said water levels were reducing, but warned the volume of water was “unprecedented”.

Images captured from the Ebbsfleet entrance to the tunnel showed water tankers at the site.

A Met Office spokesman told the PA news agency the problem was unlikely to have been caused by bad weather because there had been “no heavy rain overnight or in the area”.

Ebbsfleet International, which is on the other side of the flooded tunnel from London, used to be served by Eurostar, but no international trains have stopped since March 2020, due to the coronavirus pandemic.

The flooding also disrupted Southeastern Railway trains, which will run a reduced service between Ashford and St Pancras International.

Passengers stranded at St Pancras said the disruption had ruined their New Year’s Eve plans, which included going to Disneyland, seeing the Eiffel Tower, and going to an ice hockey match.

Two newlyweds visiting from New York said their dream of seeing in the new year at Disneyland Paris was in tatters.

Nicole Carrera, 29, and her husband Christopher, 31, had to rebook for a 2.30pm outbound train on Sunday.

Ms Carrera, who works for cosmetics firm L’Oreal, told the PA news agency: “We’ve been in London since Wednesday and we wanted to leave today because we were actually supposed to go to Disney Paris tomorrow for New Year’s Eve.

“So obviously those plans are ruined because now we won’t get into Paris tomorrow until about 6pm.”

Christina David, 25, and Georgina Benyamin, 26, from Sydney, have been travelling in Europe for about three weeks and their planned final stop is Paris, where they hoped to spend New Year’s Eve and New Year’s Day before flying home on January 7.

Ms Benyamin said: “Now we have to book a hotel to stay for the night here.”

Ms David added: “We’ve got nowhere to stay.”

Ms David went on: “We paid for an expensive hotel with an Eiffel Tower view.”

Ms Benyamin added: “We travelled Europe on a budget and then like once we hit New Year’s we’re going to go hard, watch Paris light up, I don’t think that’s going to happen… I’m going to cry.”

Matthew Hulls, 40, from Colchester, was “devastated” and forced to head home after a surprise trip to Cologne for his partner was cancelled because of flooding disruption to Eurostar trains.

The railway worker had booked his partner a VIP ticket to a hockey game in Cologne on New Year’s Eve.

“My partner and I are big ice hockey fans of the local team and I’d purchased VIP tickets as a surprise for her, so (I’m) pretty devastated,” he told the PA news agency.

“I had to work over Christmas, so had some special plans to compensate for that with my partner, but now it’ll be attempts to get refunds, if at all possible, and claims through my insurer – (it’s) not about the money, devastated to be missing out on what we had planned.”

Separately, there was major disruption to Thameslink services through London and across the South East due to “a shortage of train crew” which will continue into Sunday, the operator said.

The Met Office has warned there could be disruption to domestic journeys this weekend, as windy conditions sweep across the UK.

A warning for rain and snow has been issued for much of Scotland.