Parts of the UK are being battered by rain and fierce winds, as weather forecasters warn worse may be to come.
Winds of up to 82mph (130km/h) have brought down trees in Wales and south-west England and left 10,000 homes without electricity.
There are 36 flood warnings in place in England and Wales and it is feared water could spill over sea walls when high tides peak.
Roads were also disrupted and a 50mph limit was in place on some rail lines.
Environment Agency chief executive Baroness Young told BBC News: "Along the coast from the South West, almost as far as Kent, we could see the sea coming over the sea walls and that's when we really could have difficulties.
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We have had very heavy rain and wind overnight
"We are saying to people, stay away. It's very impressive to watch but these waves could come over at any time."
She said the first wave of the storm had resulted in only localised flooding but there was "more to come" as "two big bands" of severe weather were to sweep the country.
However, she said areas at risk were "as well prepared as is possible" to deal with potential problems, with evacuation plans in place.
Small-scale flooding has affected parts of the South West, with residents putting out sandbags to protect homes in parts of Devon and Cornwall.
The Environment Agency in Devon said the morning high tide had not been as bad as predicted and had passed without major incident, though there had been minor flooding around the coast.
However, it said high winds and large waves were still a threat.
High winds have also caused considerable damage and disruption, blowing off garage roofs in Devon and west Wales, uprooting trees and bringing down power lines.
Fallen trees are a danger on the roads (Pic:Terry Simon Aldous)
7,000 homes in south-west England and 3,000 in Wales are without power.
The Tamar Bridge between Devon and Cornwall has been closed to high-sided vehicles.
Wind speed of 82mph recorded in Berry Head in Brixham, south Devon.
The Old Severn Bridge between England and Wales is partly closed because of high winds.
The Sheppey Crossing and the QE2 Bridge across the Thames between Essex and Kent are both closed.
Tugs had to tow an 11,000-tonne tanker into port after she got into difficulties in the Solent.
In London a woman was knocked unconscious after a hoarding was blown down at West Hampstead railway station.
Elsewhere in the UK, high winds are expected to cause disruption, with wind speeds of 42mph recorded at Heathrow, 63mph on the east coast of Northern Ireland, 49mph in Crosby, Merseyside, and 46mph in Birmingham.
The RAC is advising drivers to be prepared for hazardous driving conditions over the next few days.
Several roads are blocked in Wales and south-west England and flooding on the Surrey stretch of the M25 is causing severe delays.
The Met Office warns rail delays are likely, with the worst weather expected to strike on Monday afternoon. A 50mph speed limit is in force on some lines and there are severe delays to some London trains because of weather disruption in Surrey.
British Airways cancelled several short-haul and domestic flights from Heathrow Airport on Sunday night, and both Heathrow and Gatwick advised travellers to check with airlines before leaving home.
P&O Ferries cancelled a Sunday sailing from Portsmouth to Bilbao, and another from Bilbao to Portsmouth on 11 March. Channel crossings to France and crossings between Wales and Ireland have been cancelled and the Port of Dover is closed due to hurricane-force 80mph winds.
Parts of north-east England and Scotland have been hit by snowfall as well as high winds with snow ploughs needed to keep some roads open.
It was expected to turn to heavy rain later on Monday but early flurries, coupled with driving winds, caused treacherous conditions on the A66 between County Durham and Cumbria.