Thousands of people were evacuated from their homes as a tidal surge hit coastal towns along the east coast of Britain.
The fierce Atlantic storm - which has already claimed two lives - caused widespread disruption.
The surge, predicted to be the worst for more than 60 years, hit the north Norfolk coast early in the evening and was expected to head south throughout the night.
The Environment Agency (EA) has issued a number of severe flood warnings - the highest category, which are only issued when flooding poses a danger to life - covering coastal areas in East Anglia, the Midlands and Kent.
Humberside Police said a search and rescue operation had been launched for three people who may have fallen into the River Humber close to Flixborough.
The force warned the public not ignore flood warnings, saying some people had been risking their lives by running into the tide.
One man died after he was struck by a falling tree in a park in Retford, Nottinghamshire, and a lorry driver was killed when his HGV toppled on to a number of cars in West Lothian, Scotland.
The Army was called in to assist firefighters and police in Norfolk.
Across the country more than 100,000 properties were hit by power cuts as winds of up to 140mph battered powerlines.
Northern Power Grid said 20,000 properties were affected in the North East, Yorkshire and North Linconshire.
Communities in Suffolk, Essex and Kent were bracing themselves as police said the surge had arrived an hour earlier than expected.
More than 10,000 homes on the coast have been earmarked for evacuation after officials warned that the lives of people in the regions could be at risk.
Humberside Police warned the public "the worst is not over yet" with the further disruption expected with the morning tide.
Describing the storm as a "critical incident", it said anybody who ignored warnings risked putting themselves in a life-threatening situation.
A spokesman added: "Concerns have already been raised following reports of people at Cleethorpes running into the tide and standing at the side of the sea to see what is happening.
"The consequences of this are severe and the force of the tide and the wind could take those people away, with nothing anyone can do to stop it."
In Norfolk, 9,000 homes were evacuated, mainly in the Great Yarmouth area, as officials attempted to stem the damage from the coastal surge.
The Ministry of Defence said 60 Light Dragoons, based at the Swanton Morley Army base in Norfolk, were helping with the effort.
At Blakeney in north Norfolk, the water breached the quay at about 5.30pm.
Within 30 minutes the floods had advanced some 165ft (50m) up the village's main street. Water reached window height and at least one car was seen being swept away.
Allan Urquhart, who has lived on the seafront for eight years, took a rowing boat to the King's Arms pub to collect a friend.
He said: "I'm going to row back to the house and we'll stay upstairs tonight.
"We've put sandbags in place so hopefully we'll be OK. I'm as confident as I can be.
"This is the worst flooding I've seen so it could be a difficult night for lots of people."
Staff were seen baling water from the window of the King's Arms as the surge reached bar height.
Cliff Park High School, which was being used to hosue evacuees near Yarmouth, was full by mid-evening, Norfolk Police said.
A further 1,000 properties are expected to be evacuated in affected areas in Suffolk.
Officials are setting up emergency accommodation facilities and handing out sandbags to help people protect their homes.
A spokesman for Suffolk Police said the surge was expected to be an hour earlier and slightly higher than predicted.
Residents from more than 60 streets around Jaywick in Essex have been advised to leave their homes, Essex Police said.
In Kent, more than 500 properties were evacuated in areas including Sandwich, Seasalter and Faverhsham.
The EA has issued more than 230 flood alerts across England and Wales, including 43 severe flood warnings which are only issued when flooding poses a "significant threat to life".
Communities from Northumberland to the Thames Estuary and Kent, in addition to those on the Irish Sea coast from Cumbria down to Cheshire, could see significant coastal flooding.
A spokesman said that in some areas sea levels could be higher than those during the devastating floods of 1953 - which battered the east coast of England and claimed the lives of hundreds of people.
Defences built since then - including the Thames and Hull Barriers - mean that many parts of the country are much better protected, he said.
However, some coastal flood defences could be "overtopped" by the combined effect of high tides, high winds and a large tidal surge, he added.
The Met Office said the Atlantic storm brought severe gales of between 60mph and 80mph across Scotland and northern parts of England, and some mountainous regions in Aberdeenshire and Inverness-shire reported speeds of around 140mph.
The adverse weather has also caused chaos to the transport network, with rail services for Scotland and parts of the North of England suspended.
Environment Secretary Owen Paterson, who chaired two Cobra meetings, said: "It is really important that people take steps to prepare for flooding, which is likely to occur overnight.
"Clearly our priority is public safety and I urge people to act on the advice from the environment agency, police and local agencies."
:: People are being urged to check the Environment Agency website or follow @EnvAgency and #floodaware on Twitter for the latest updates on flood warnings.