Dozens of people have been forced to leave their homes as Cumbria battles severe weather conditions, with 200mm (8in) of rain predicted for some areas.
Six severe flood warnings are in place at Keswick, Cockermouth, Eamont Bridge, Southwaite and Burneside.
More than 20 schools have been closed across the county and a nursing home in Keswick was evacuated as a precaution.
Police said almost 100 people have sought shelter at rescue centres set up in Keswick and Cockermouth.
Up to 40 residents in the Waterloo Street and Gote Street areas of Cockermouth have moved to one of the centres as water up to 3ft (1m) deep entered properties.
About 50 police officers and mountain rescue volunteers have been helping evacuate people in Cockermouth, where the River Derwent burst its banks.
The town's High Street has been partially flooded.
The Environment Agency said the River Cocker had also burst its banks.
More than 20 riverside properties in Kendal were evacuated, including a residential care centre.
Allerdale Council said it had received more than 100 requests for sandbags in Keswick and Cockermouth.
The River Kent at Burneside burst its banks early on Thursday, with the village now virtually cut off, with residents reporting cars covered by floodwater.
Cumbria Police said it had received 90 flood-related calls for help, while Cumbria Fire and Rescue Service said it had responded to 150 incidents, including multiple rescues.
Several major roads have been closed, including parts of the A591, the A6 and the A595.
Ch Supt Kevin McGilloway said: "We are asking people not to travel unless it is absolutely necessary.
"Pedestrians in areas where there are floods, such as Cockermouth, Keswick, Penrith and Kendal, are being urged not to attempt to walk through floodwater.
"The key message is for people who are affected by the floods to be prepared, to try and protect any properties that are liable to flooding.
"Look out for one another including vulnerable friends and neighbours."
Almost 5,000 workers at the Sellafield nuclear reprocessing plant have been sent home because of difficult road conditions.
A spokeswoman said the non-essential workers were leaving in a "phased release".
The Forestry Commission said it had closed its facilities at Grizedale and Whinlatter because of the worsening weather conditions.
A spokesman said one tree had already come down near Armathwaite and the wet ground could mean more being uprooted.
Residents and businesses in Carlisle, which was hit by devastating floods in 2005, have also been bracing themselves for flooding.
Defences installed after the 2005 event are expected to offer protection to more than 2,500 properties in the city.
Environment Agency and local authority staff worked throughout the night to erect temporary defences for an extra 400 properties.
Agency spokesman Craig Cowperthwaite said persistent downpours on Thursday would fall on ground saturated by overnight rain.
He said: "The rivers nearest the fells will rise this morning, but for the likes of Carlisle it will be afternoon before it gets to high levels.
"People need to be vigilant all day and look out for flooding on roads when they are out and about in the county."
Earlier Cumbria County Council moved all residents at Ravensfield Residential Home, on High Hill in Keswick, to safety because of the threat of flooding.
The Met Office said between 50mm and 70mm (2-2.75in) of rain could fall in widespread parts of the county before 0600 GMT on Friday, with the possibility of 200mm (8in) across the most exposed fells.
Twelve flood warnings, the second most serious of the Environment Agency's alerts, have also been placed throughout the county.
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