More than 2,000 properties in two Manchester suburbs are being evacuated as heavy rainfall from Storm Christoph continues to batter parts of England.
Severe flood warnings, meaning there is a danger to life, have been issued for Didsbury and Northenden, where many homes lie close to the River Mersey.
The Environment Agency confirmed the properties were being evacuated in both areas.
Greater Manchester Police said officers would be in touch with those affected.
The force had already declared a major incident in preparation for the storm.
Assistant Chief Constable Nick Bailey said: "We have an evacuation plan in place to set up those who have been displaced in temporary accommodation.
"I think it's important to stress that if you are contacted and advised to evacuate then we would strongly urge you to do so."
Manchester City Council has confirmed those who need to stay with friends and family temporarily due to flooding will not be in breach of coronavirus lockdown rules, which allows for exceptions including to escape the risk of harm.
The council said it had set up a "Covid-safe emergency rest centre" at Wythenshawe Forum.
Severe flood warnings have also been issued for Whinney Brook and Dovers Brook in Maghull, Merseyside.
A spokesman for Sefton Council said heavy rainfall is "expected to impact the Sefton Lane, Sefton Drive, Claremont Avenue and old Racecourse Road areas [of] Maghull".
Residents in these areas are being urged to vacate their homes immediately and a temporary rest centre has been set up at Meadows Leisure Centre, the spokesperson added.
Prime Minister Boris Johnson earlier urged people to follow evacuation advice, adding Manchester, where up to 3,000 properties are feared to be at risk, was an area of concern.
People living across north-west England are being urged to prepare for the risk of significant flooding for the rest of this week, the Environment Agency added.
Train operator Northern has cancelled the majority of its services due to "increasingly poor conditions".
Regional director Chris Jackson said: "Unfortunately the situation is only getting worse.
"We have had to make the difficult decision to ask our customers not to travel for the rest of the day."
Transport for Greater Manchester said Palatine Road in Manchester was closed between Barlow Moor Road and Princess Parkway due to heavy flooding in the area.
Slag Lane in Lowton, Warrington, was closed between Plank Lane and Byrom Lane due to "significant flooding", it said.
Warrington Road at Greenfold Way in Leigh was also impassable, Wigan Council said.
Greater Manchester mayor Andy Burnham said car parks had been opened for people to safely move their cars away from at-risk areas.
"If people need to leave their property to protect themselves and family they are able to do so but we hope they do it in a Covid-safe way," he said.
Greater Manchester's Chief Fire Officer Dave Russell added: "There should be no attempt to move along road networks when there is standing water. Don't make any journeys at all unless absolutely necessary to do so."
The Environment Agency has issued more than 60 flood warnings, meaning flooding is expected and immediate action required, while there are also more than 180 flood alerts, meaning flooding is possible.
Two other police forces - Cheshire and South Yorkshire - have also declared major incidents.
Cheshire Police earlier moved 33 people from houseboats in Hayhurst Marina in Northwich, Cheshire, for their safety as water levels rose in the River Weaver.
They were offered accommodation in nearby hotels.
More than 120mm (nearly 5in) of rain has already fallen in some parts of England, with 123.4mm at Honister Pass in Cumbria in the 24 hours up to 06:00 GMT on Wednesday.
Downing Street said Covid-secure evacuation centres would be made available to those forced to leave their homes as a result of flooding.
Judy Hobson, BBC North West environment correspondent
I'm standing in the middle of a major road - Palatine Road - in south Manchester that has been closed.
The River Mersey is so high and fast flowing that the bridge over it has been closed to traffic for safety reasons.
Northenden high street is also closed as the River Mersey affects homes right across south Manchester.
Now this area has a flood warning across it. People haven't been asked to leave but they have been asked to move their cars and been told to start taking their valuables upstairs. Things like medicines too.
This is very difficult for residents - people keep coming out and asking police if they have to leave yet.
They're being told to know where their gas and electricity supplies are. If you have to leave you'll have to turn them off.
This is going to be a very difficult night for them and it's still raining very heavily.