Severe gales and heavy showers in southern England and Wales are likely to cause further travel chaos on New Year’s Eve, amid severe disruption on parts of the rail network.

Eurostar services resumed shortly after 8am on Sunday after “unprecedented” flooding in a Thames tunnel caused long delays and cancellations and an estimated backlog of more than 30,000 passengers.

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

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

A yellow warning for wind with severe gales and heavy showers along the south coast of England, the West Country and southern Wales is likely to add to travel problems.

The Met Office warning said: “Gales or severe gales in association with heavy showers may lead to disruption to transport and infrastructure.”

It said “delays to road, rail, air and ferry transport are likely” from 10am to midnight, adding: “Probably some bus and train services affected, with some journeys taking longer.”

The Met Office also warned that “some coastal routes, seafronts and coastal communities will be affected by spray and/or large waves”. Power cuts were also possible because of the high winds, it added.

Eurostar warned passengers to expect further delays on Sunday. In a statement, it said: “Our stations will be extremely busy due to today’s disruption. 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. 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 issue was believed to have been caused by a burst pipe feeding the tunnel’s fire safety system, a water company said. Thames Water said it believed the flood was caused by a “fire control system and not a Thames Water pipe”.

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

There was also major disruption to Thameslink services through London and across south-east England due to “a shortage of train crew” that would continue into Sunday, the operator said.

Thameslink said its services would be severely reduced or cancelled. It advised passengers to seek alternative travel options on the line from Brighton to London and Bedford to London.