Greater Manchester Police has declared a major incident as Storm Christoph is set to batter the UK.
Police have urged residents to be prepared to evacuate despite the Covid-19 lockdown - as "where there is a risk of flooding, that is clearly essential".
Assistant Chief Constable Nick Bailey, who is chair of the GMP's strategic coordination group for Storm Christoph, has said if people need to evacuate their homes due to flooding "then that is the priority.
He said: "In order to ensure that we're as prepared as possible for the heavy rainfall expected from Storm Christoph, we have declared a major incident.
"The safety of the public is our number one priority and we're continuing to work alongside partner agencies across the region.
"Whilst we appreciate that everyone has been told to stay home due to the Coronavirus pandemic, we want to make it clear that should members of the public need to evacuate to protect themselves due to flooding then that is the priority and you should follow your local authority's advice regarding evacuation.
"Coronavirus remains a threat to everyone's health and people should not leave their homes unless it is absolutely essential, but where there is a risk of flooding, that is clearly essential and we're working with our partners to ensure that people can do this as safely as possible.
"For anyone that needs to evacuate, we'd ask that you remain very aware of Covid-19 and continue to follow the government guidance around Hands, Face, Space as much as possible and limit your contact with other people."
A number of flood alerts have been issued across Greater Manchester and Cheshire as Storm Christoph brings torrential downpours to the region.
The Met Office has issued an amber ‘danger to life’ weather warning for heavy rain and flooding for large parts of northern England.
And the Environment Agency has also issued a number of flood alerts for parts of the region, meaning that flooding is possible in those areas and that residents should be prepared.
Assistant Chief Constable Bailey added: "We would continue to urge anyone with concerns about flooding in their area to contact their local authorities who will be able to sign-post you to the most appropriate information and support.
"Partner agencies are working hard on local plans to ensure that people living in potentially vulnerable areas are notified at the earliest opportunity.
"Heavy rainfall is expected from later today and that could cause flooding in several areas across Greater Manchester - we are preparing for this and are continuing to monitor the situation very closely. We will continue to provide updates as often as we can."
Authorities are on high alert across the UK as Storm Christoph is expected to dump two months' worth of rain and bring more snow for some.
The Met Office is warning of more snow tomorrow in a Storm Christoph 'double whammy' alert.
Parts of Scotland are now on high alert, with the weather agency predicting rain will increasingly turn to snow during Wednesday and overnight into Thursday.
Met Office forecaster Aidan McGivern said up to 5cm of snow could fall in the Southern Uplands this evening due to lingering cold air.
"That cold air still there across northern Scotland and that will start to sink southwards somewhat to mainly bring a snow threat to the hills of Northern Ireland and southern Scotland during Tuesday evening," he said.
Mr McGivern said: "At lower levels it will of course be rain and some very heavy rain starting to emerge there across northern England and North Wales, combine that with the snow melt expected and you're looking at a serious risk of flooding."
People are being urged to prepare with an amber warning for rain to last through to Thursday for central northern England, affecting an area around Manchester, Leeds and Sheffield and stretching down to Peterborough.
A major incident has also been declared in South Yorkshire with sandbags handed out in flood-risk areas.
Heavy rain is expected to first hit across the country overnight tonight, with homes and businesses likely to be flooded.
Catherine Wright, acting executive director for flood and coastal risk management at the Environment Agency, said rain falling on wet ground means a "very volatile situation" is on the cards.
"We are expecting significant flooding to occur on the back of that weather," she added.
Storm Christoph is set to bring 48 hours of flooding hell with more than a month's rainfall likely to fall in just a few days.
People are being urged to prepare as an amber weather warning for rain was issued by the Met Office for Tuesday to Thursday for central northern England, affecting an area around Manchester, Leeds and Sheffield and stretching down to Peterborough.
Separate Met Office yellow warnings for rain have been issued for Northern Ireland, Wales, southern Scotland and the rest of England for the next two days.
The Met Office warned homes and businesses could be flooded, causing damage to some buildings and fast flowing or deep floodwater is possible, causing a danger to life.
This morning the Environment Agency has also issued 15 flood warnings and 117 flood alerts.
The most serious weather warning - amber for rain - has been in place across parts of the Midlands and northern England since Tuesday morning, alongside less serious yellow warnings for rain across Wales, Northern Ireland, northern England and southern Scotland.
The highest rainfall recorded overnight was in Aberllefenni, west Wales, where 35.4mm fell between midnight and 8am on Tuesday.
Of the areas in the amber warning zone, Bolton in Greater Manchester has seen the most rain so far, with 24.4mm over the same period.
By Wednesday, the yellow warnings for rain will stretch south to additionally cover all of England, all of which remain in place until midday on Thursday, alongside the more serious amber warning in central England.
Eastern Scotland is also facing a yellow warning for snow and from Wednesday afternoon through to Thursday lunchtime, with the threat of travel delays, power cuts and rural communities being isolated.
Delays or cancellations to train and bus services are possible and flooding could lead to difficult driving conditions and some road closures.
Some communities may be cut off by flooded roads and there could be power cuts in homes.
Chief Meteorologist Dan Suri said “Following a cold spell where the main hazard was snow, our focus now turns to notably heavy rain moving across the UK this week.
"Some locations could see over 100mm of rain falling through the course just a couple of days with up to 200mm possible over higher ground.
"These amounts of rainfall along with snow melt present a real threat of flooding and people should keep a close eye on flood warnings from the Environment Agency and Natural Resources Wales."