Police are to begin evacuating people from their homes as Storm Christoph continues to bring “significant” rainfall across the UK.
Greater Manchester Police said about 160 people will be advised to leave their homes in Didsbury and move into temporary accommodation on Wednesday evening.
It comes as heavy rain continues to fall across England, with many rivers at “dangerously high levels”, the Environment Agency said.
Homes in Ruthin, Denbighshire, have also been evacuated due to flooding, North Wales Police tweeted.
Amber and yellow weather warnings are in force until Thursday for the storm, which is 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.
Greater Manchester Police assistant chief constable Nick Bailey said a flood basin in Didsbury, which takes water from the River Mersey, was full and will “over-top in the next few hours”.
“As a result, we will be issuing a flood warning to homes,” he said.
“This will be through texted flood alerts to some people and police officers, PCSOs, firefighters, and volunteers will be knocking on doors.
“We have identified about 160 people that will be moved. There will be provision at Wythenshawe Forum and hotels are being used.
“Some of those that are being evacuated will also be Covid-positive or isolating at home.”
Mr Bailey said up to 3,000 properties in Greater Manchester could be affected by flooding, with a peak expected at 11pm on Wednesday.
Two “severe” flood warnings, meaning there is a danger to life, have been issued by the Environment Agency for the River Mersey at East and West Didsbury, and Northenden.
North Wales Police said its officers were helping the fire service to evacuate homes in Ruthin, 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.”
Downing Street has said Covid-secure facilities will be available for any people forced to evacuate as a result of the weather.
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.”
It comes as 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 122 flood warnings across England, with 222 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 midday on Thursday, 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.
A colder day is in store for many of us on Thursday in the wake of #StormChristoph— Met Office (@metoffice) January 20, 2021
If you need to travel, be aware of icy patches in places to begin the day, especially in the northwest and also the risk of #flooding in some areas
Further heavy #snow is likely across Scotlandâ ï¸ pic.twitter.com/cZxa62FX2S
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”.
The company’s regional director, Chris Jackson, said: “Unfortunately the situation is only getting worse and we have had to make the difficult decision to ask our customers not to travel on the Northern rail network in the North West for the rest of today.”
Mr Jackson urged commuters wishing to use the service on Thursday morning 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.
The meteorologist said: “While rain remains the main hazard in the south, further north we’ve got snow and ice remaining a risk.
“The system will work its way through, we are expecting significant totals of rainfall and when you combine that with snowmelt it can lead to localised flooding across the affected regions.”
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.
Public Health England (PHE) has issued a cold weather alert for the North East, North West, and Yorkshire and the Humber from 9am on Thursday to January 25.
Dr Owen Landeg, principal environmental public health scientist at PHE, urged people to “keep looking out” for frail or older neighbours and relatives, particularly those living alone or with a serious illness.
People were preparing for rising floodwaters in West Yorkshire on Wednesday morning, with towns in the Calder Valley laying out sandbags and flood wardens monitoring water levels.