Some 2,000 properties in Greater Manchester will be evacuated overnight due to flooding caused by Storm Christoph, the city council said.
Police and firefighters were working with Manchester City Council to evacuate homes in East Didsbury, West Didsbury and Northenden on Wednesday evening.
People have also been asked to leave their homes in parts of Ruthin, North Wales, and Maghull in Merseyside due to rising floodwaters.
It comes as heavy rain and snow continues 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, have been issued by the agency for the River Mersey at Didsbury and Northenden, and in Maghull.
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 has 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 will 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 would “over-top in the next few hours”.
“As a result, we will be issuing a flood warning to homes,” he said.
“We have identified about 160 people that will be moved. There will be provision at Wythenshawe Forum and hotels are being used.”
He said some of those being evacuated will have tested positive for coronavirus.
Mr Bailey said up to 3,000 properties in Greater Manchester could be affected by flooding.
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.”
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.
A temporary rest centre has been set up at the Meadows Leisure Centre.
Downing Street said Covid-secure facilities will 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— Met Office (@metoffice) January 20, 2021
Here are the latest rainfall totals since midnight on Tuesday 👇 pic.twitter.com/7qYyDj1qiU
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 130 flood warnings across England, with 225 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.
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.
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.