Police have urged people not to drive to “see the floods” as heavy rainfall has forced thousands to evacuate their homes.
North Wales Police said its officers were helping the fire service to evacuate homes in Ruthin, Denbighshire, after the storm brought heavy rainfall to much of the UK on Wednesday.
Urging people to avoid the area, the force tweeted: “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.”
Police and firefighters in Greater Manchester have also been working with council staff to evacuate homes in the areas of East Didsbury, West Didsbury and Northenden.
The city council said about 2,000 properties would be evacuated overnight, while Greater Manchester Police said up to 3,000 properties were at risk of being affected by flooding.
Watch: UK weather - Storm Christoph to be replaced by temperatures as low as -10C - but more floods possible next week
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".
He said facilities would be provided at Wythenshawe Forum and hotels in the area for those needing to evacuate, including some who will have tested positive for coronavirus.
People have also been asked to leave their homes in Maghull, Merseyside, following “unprecedented” water levels at Dover Brook, near the River Alt.
A temporary rest centre has been set up at the Meadows Leisure Centre.
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.
Boris Johnson has urged people to heed the flood warnings and evacuate their properties when told to do so, as Downing Street said Covid-secure facilities will be available for anyone forced to leave their home as a result of the weather.
The prime minister 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.
It came after he 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 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.
Additional reporting by PA
Watch: Storm Christoph - Boris Johnson warns 'more flooding to come' as severe warnings remain in place