Six people were rescued from cars in three separate incidents in Devon
A period of "exceptional weather" bringing rain, wind and high tides is set to hit the UK, Environment Secretary Owen Paterson has said.
It came as the Environment Agency issued several severe flood warnings - indicating a danger to life - for south-west England on Friday morning.
Tidal flooding is expected in "numerous locations" due to large waves, high tides and strong winds.
Mr Paterson said ministers were working to ensure all agencies were prepared.
He was speaking after chairing a meeting of the Cobra emergency committee, in which the UK's flood response was discussed.
Mr Paterson said the coast would be dangerous.
Cobra, named after Cabinet Office Briefing Room A in Whitehall, brings together ministers, civil servants and others such as the police and Environment Agency - depending on the nature of the emergency it is responding to.
Dozens of flood warnings are in place in England, Wales and Scotland.
The Police Service of Northern Ireland has said there is potential for flooding in a number of areas across the country, including Belfast, as a result of a tidal surge expected at midday on Friday.
In England, severe flood warnings were issued for coastal areas of Devon, parts of the River Taw and River Torridge and communities near the Taw Torridge Estuary.
High water is expected to be about 07:00 GMT on Friday. Conditions are expected to be at their worst during that time and for two to four hours either side of it.
The severe flood warnings have also been issued for parts of the north and south Cornwall coasts.
BBC forecaster John Hammond explains the latest
weather systems that are causing concern
The Environment Agency's head of strategy, Pete Fox, said: "We are expecting flooding along the west and south coasts of England and Wales, due to a combination of strong winds, large waves and high tides, from the early hours of Friday and into the weekend.
"Coastal paths and promenades could be highly dangerous as there is an increased risk of being swept out to sea. People are warned to stay away from the shoreline."
Mr Paterson chaired meetings throughout Wednesday to ensure the Environment Agency and local councils "are on the ground and offering all possible support to their communities".
"We remain in touch with local councils in at-risk areas," he said.
"With a number of flood alerts for Thursday, including several areas which have previously been flooded, I urge everyone in affected areas to sign up to Environment Agency flood warnings and follow the advice issued."
Thousands of homes have suffered power cuts due to the recent storms, with some cut off for several days, while numerous properties and roads have been flooded.
Many of the flood warnings on Wednesday - and those issued for Thursday - were in south-west England, where Devon and Cornwall Police appealed for people not to enter the sea during the bad weather.
Flooding disrupted a number of train services on Thursday morning, with no services running between Teddington, south-west London, and Shepperton in Surrey.
There was also disruption between Fareham and Southampton Central/Eastleigh in Hampshire, because of flooding at Hedge End and Botley.
In Wales, the River Towy in Carmarthen burst its banks after continuing heavy rain.
The Thames Barrier in London has been closed to protect people and property along the river, the Environment Agency said.
The bad weather has led to power cuts for 319 properties in Surrey and Hampshire, energy supplier SSE said.
A woman drowned in the sea near Croyde, north Devon, on Tuesday. It is believed she had been swimming or surfing.
And the search for a 27-year-old man washed out to sea near Porthleven, Cornwall, in the early hours of New Year's Day was called off after a body was found on the beach.
Rescue teams have also been searching for:
Severe flooding hit several Devon villages on Wednesday and six people - including a baby - were rescued from cars in three separate incidents in Fenny Bridges, Ford Bridge and Avonwick.
The Met Office has issued yellow warnings - the lowest of its three levels - for rain and high winds on Friday in Northern Ireland and western parts of Scotland, Wales and England.