A second red weather warning - danger to life - has been issued by the Met Office as Lancashire and Yorkshire are hit by severe floods.
Two of the Met Office's rare "take action" alerts are currently in place and the Environment Agency (EA) has issued seven severe warnings for the North West.
Residents in Whalley and Ribchester in Lancashire were told to abandon their houses when flood waters poured through the streets after torrential downpours.
Todmorden in West Yorkshire has also been hit and the waters are continuing to rise as the rain keeps falling.
Resident Lee Fraser, who lives on Halifax Road, said the road between the town and the neighbouring village of Hebden is submerged.
"It's getting worse and worse, it's been raining really heavily since last night," he added.
"The siren went off at about 7am this morning and 10 minutes later everything started flooding.
"A lot of people are moving their stuff upstairs in their houses and the police came and closed the roads.
"It's absolutely tipping it down, so it's only going to get worse by the look of it."
Forecasters said up to 4.7ins (120mm) of rain could fall in some areas already saturated by wave after wave of winter squalls. The average rainfall for the whole of December in the North West is 5.7ins (145mm).
The EA has issued 87 warnings and 27 alerts for flooding in Yorkshire on Saturday and Sunday.
Heavy rains are expected to affect Calderdale, Airedale (from Skipton to Leeds) and North Yorkshire including York, Pateley Bridge and Catterick.
A spokesman said: "The rain has fallen on areas where the ground is already saturated and river levels are very high.
"Our teams are out working with partners to support communities and reduce the risk of flooding as far as possible.
"We are urging people to listen out for sirens and stay tuned to local media and take action when necessary."
Flood sirens have already been sounded at Walsden, Todmorden, Hebden Bridge and Mytholmroyd in Calderdale.
Lancashire Fire and Rescue Service warned people to stay away from the Whalley and Ribchester areas.
"A severe flood warning means danger to life. It doesn't mean 'come and have a look'. Please don't come to visit Whalley or Ribchester now," the service said in a tweet.
Lancashire Fire also posted details of an emergency evacuation centre for evacuated residents.
A number of Boxing Day football and racing events were called off because of the floods, including the Blackburn Rovers fixture.
The match between Blackpool and Oldham was postponed, as were the games between Hartlepool and Notts County, Morecambe and Mansfield and Accrington and Carlisle.
Officials at Wetherby races cancelled both days of their Christmas card and Saturday afternoon's meeting at Limerick has also been abandoned.
The severe flood warnings - the EA's highest level of warning - are for two locations on the River Ribble at Ribchester, three locations on the River Calder at Whalley and two on the River Wyre at St Michaels.
Around 125 flood alerts and 190 warnings have been issued by the EA, mainly for the North West, North East and Wales.
The Government's emergency Cobra committee met on Christmas Day while a company from the 2nd Battalion, Duke of Lancaster's Regiment, helped communities across the North West build miles of temporary flood defences.
The EA said 85% of the country's temporary flood barriers had been sent to Cumbria, where rainfall has smashed records, and the Lakeland region braced itself again ahead of the deluge.
The Scottish Environment Protection Agency issued five flood alerts and 16 flood warnings.
Flood warnings extended across northern Britain, including the Calder in West Yorkshire and the Ribble, Wyre and Wenning in North Yorkshire. Pendle Water, Pimlico Brook, the Burrow and Hellifield Beck were also at risk of bursting their banks, the EA warned.
The Met Office issued a yellow warning of rain for parts of north Wales, northern England and southern Scotland.
Floods Minister Rory Stewart said that rainfall levels in the flood-hit areas were unprecedented.
"We're looking potentially again today at maybe a month's rainfall coming in a day. That's falling on ground that's very saturated. As the rain falls, the rivers respond very quickly," he told the BBC Radio 4 Today programme.
In the Outer Hebrides, CalMac ferry sailings were cancelled for the day in North Uist and South Uist. Services have also been affected on Bute and the Isle of Lewis.
Lancashire has been hit by the downpours that were forecast to fall in Cumbria, Lancashire Police said.
"Lancashire is experiencing the rainfall expected to fall in Cumbria and a further 50mm to 80 mm may fall in the next six to nine hours," the force tweeted.
"The band of rain currently over Lancashire is expected to move northwards in the afternoon before returning in the early to mid-evening."