Hundreds of people were being evacuated from their homes overnight as Storm Christoph caused widespread flooding across the UK.
Some 2,000 properties in the East Didsbury, West Didsbury and Northenden areas of Greater Manchester were evacuated on Wednesday night because of rising water levels, the city council said.
People were also asked to leave their homes in parts of Ruthin, North Wales, and Maghull in Merseyside.
It comes as heavy rain and snow continued to fall across England and Wales, with many rivers at "dangerously high levels", the Environment Agency said.
Four "severe" flood warnings, meaning there is a danger to life, were issued by the agency for the River Mersey at Didsbury and Northenden, and in Maghull.
Amber and yellow weather warnings were in force until Thursday morning for the storm, which was also threatening to bring up to 30cm of snow to northern areas.
Prime Minister Boris Johnson earlier urged people to heed the flood warnings and evacuate their properties when told to do so.
A Manchester City Council spokesman told the PA news agency that around 2,000 properties would be evacuated.
Greater Manchester Police assistant chief constable Nick Bailey said a flood basin in Didsbury, which takes water from the River Mersey, was full and was expected to "over-top" at some point during the night.
An emergency rest centre was set up at Wythenshawe Forum and hotels were also being used for those forced to flee.
North Wales Police said its officers were helping the fire service to evacuate homes in Ruthin, Denbighshire, and urged people to avoid the area.
The force tweeted: "Officers have been called to assist @DenbighshireCC and @NWFRS in #Ruthin, where some homes are being evacuated.
"Regrettably, people who do not live locally are driving to the area to 'see the floods'. Please do not stretch our resources by adding to the problem."
— Jack Horsefield (@horsefield_jack) January 20, 2021
Meanwhile, residents in Maghull were advised to leave their properties as soon as possible after a severe flood warning was issued, Sefton Council said.
A council spokesman said heavy rain had led to raised water levels and flooding from the River Alt which was set to increase.
"Water levels at Dover Brook, near the River Alt, reached 2.5m today, which is unprecedented for that area, modelling from the Environment Agency, including anticipated overnight rainfall, will take that level to 3.5m," the spokesman said.
Downing Street said Covid-secure facilities would be available for any people forced to evacuate as a result of the weather.
#StormChristoph has produced some very heavy #rain across parts of the UK, with further rain to come in places
Here are the latest rainfall totals since midnight on Tuesday 👇 pic.twitter.com/7qYyDj1qiU
— Met Office (@metoffice) January 20, 2021
Mr Johnson said steps were being taken to ensure the transport and energy networks were prepared so that electricity outages would not be "severe" and that there were sufficient supplies of sandbags.
He told reporters: "There are some times where I have been to scenes where, alas, people have decided not to obey the advice and not evacuated.
"It is their right not to do so if they choose – it's always people's right to stay wherever they are.
"But it really is advisable – follow the advice. If you are told to leave your home then you should do so."
Mr Johnson chaired a Cobra crisis meeting on Wednesday after major incidents were declared in Greater Manchester, South Yorkshire, Cheshire and Derbyshire.
The Environment Agency has issued a further 137 flood warnings across England, with 227 less severe flood alerts, mainly across the Midlands and north of the country.
Almost the whole of England, Wales and Northern Ireland are subject to yellow weather warnings for rain until Thursday morning, with a more serious amber warning stretching from the East Midlands to the Lake District.
The amber alert warns of the risk of flooding and deep floodwaters which could pose a risk to life, and there are further warnings for snow and ice in Scotland.
An amber warning for snow in parts of southern Scotland warned around 30cm could fall in areas above 400m, with up to 10cm likely to accumulate in lower regions until 8am on Thursday.
Train operator Northern said torrential rain and flooding across the region had led to the closure of several rail routes, while others had suffered "significant disruption".
Commuters wishing to use the service on Thursday morning were warned to allow extra time for travel.
Met Office forecaster Grahame Madge described Storm Christoph as "quite a slow-moving system" which is bringing "a variety of weather" to the UK.
There is a risk of further snow later in the week as Storm Christoph makes its way east, with accumulations expected in Scotland, northern England and parts of Northern Ireland, Mr Madge added.