A period of "exceptional weather" bringing rain, wind and high tides is set to hit the UK, Environment Secretary Owen Paterson has said.
The Environment Agency issued several severe flood warnings - indicating a danger to life - for south-west England, Gloucestershire and Wales.
Tidal flooding is expected in "numerous locations" on Friday 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.
Three severe flood warnings, which indicate a possible danger to life, have been issued for Gloucestershire by the Environment Agency for Friday.
Three "large" Severn Bores - when the tide from the Severn Estuary is forced into narrower channels upstream - have been predicted over the next 48 hours.
The areas affected include the Severn estuary, River Severn and tidal Severn.
On the Somerset coast, nine flood warnings are in place and residents are being warned of possible tidal surges.
In Bristol, an emergency flood barrier is being deployed for the first time.
'Situation changing hourly'
High tide on the River Severn in Gloucestershire is expected between 08:00-10:00 GMT on Friday.
And with the already-swollen river the situation was changing hourly, the Environment Agency said.
Forecasters are warning that storm force winds and some of the highest tides in decades could bring further flooding misery.
Several severe flood warnings were issued, including the Gwynedd resort of Barmouth - with police urging residents to take action to protect themselves.
A rest centre is being opened for at-risk residents in the town.
Homes on an estate at St Brides Wentlooge, Newport, are also being evacuated as a precaution.
Scores of flood warnings and flood alerts were in place, covering large parts of the coast.
Earlier on Thursday, the River Towy burst its banks in Carmarthen.
It led to roads in the town being flooded - though properties escaped the floodwater.
More info on the BBC News site and pretty much every UK based news agency website.The Met Office said winds could hit 80mph on the Welsh coast on Friday, reaching storm or even violent storm force at points.
It has issued a yellow weather warning for the entire coastline of Wales, valid from midnight on Friday for 24 hours.
NRW is warning people to stay away from seafronts during the high tides on Friday.
"This is expected to be the highest tide to hit the whole Welsh coast since 1997," warned the NRW in a statement.
"While the threat extends along the entire Welsh coastline, Natural Resources Wales is particularly keeping a close eye on Newport in south Wales - specifically the Crindau area; the west coast - specifically Barmouth, Borth, Carmarthen Bay and Haverfordwest; and the north Wales coast from Kinmel Bay to the Dee estuary."
The high tide is expected at Milford Haven at about 07:20 GMT on Friday, reaching Newport by 08:15, Barmouth in Gwynedd at 09:20 and Flintshire by midday.
Wind is picking up here now, though it's been worse in the past few weeks but its expected to get stronger as the night progresses - tomorrow morning is likely to be the peak here especially as I live on the coast.
