Schools and roads are closed and drivers are facing treacherous conditions - including blizzards - and delays as a fresh blast of heavy snow causes "carnage" two weeks into spring.
Police have responded to a number of crashes - including a 24-car pileup in a "sudden microburst" of hail and snow in Lancashire - and they're urging drivers to slow down or stay home as parts of England and Scotland look like a winter wonderland in April.
Blizzard conditions were reported in strong winds in Northumberland and Cumbria, and a number of roads have been closed in Scotland where wintry conditions are wreaking havoc and snow ploughs were even getting stuck.
As much as UK weather forecast: Met Office issues SNOW warning with 4ins to blanket Britain within seven hours on Wednesday as other areas are hit by sleet, hail, thunderstorms and gales in chilly temperatures.
UK weather forecast: Met Office issues SNOW warning with 4ins to blanket Britain
The Met Office has issued a yellow warning for snow for an area of northern England and southern Scotland, while flurries were also seen down into the Midlands in the early hours.
Gritters and tractors had been working all night and morning to clear snow and ice.
Overnight, 24 vehicles were involved in a pileup as a "sudden microburst" of hail and snow hit the M55 near Broughton, which was shut for hours, said Lancashire Roads Police.
Boots store closures - 60,000 UK jobs 'at risk' after sudden US profit warning
"Thankfully no serious injuries but it was carnage," the force tweeted.
In Scotland, road closures included the A9 Inverness to Perth at Slochd, and the snow gates on the A93 at the Spittal of Glenshee and at both ends of the A957 Cairn O'Mount Road.
Police Scotland warned: "The public are asked to avoid the area if possible and thanked for their patience."
A number of schools in the Highlands were closed.
There were blizzard conditions to low levels on the A69 in Northumberland and Cumbria, Press Association photographer Owen Humphreys reported.
Poor driving conditions were reported in both counties and in Durham, and there were delays at the Tyne Tunnel because the vehicle registration recognition wasn't working due to snow.
Drivers faced delays as snow fell in Newcastle and Gateshead during the morning rush.
Cumbria County Council warned: "Please drive with care and allow extra time for your journey this morning. Snow on high roads is causing hazardous conditions. Find out the latest road conditions before you start your journey."
Durham County Council tweeted: "Please take extra care on your journey this morning."
People living in the worst-hit places have been told to avoid travelling if possible.
Wintry weather spoiled plans for golfers, where a number of courses - including Easter Moffat in Airdrie, North Lanarkshire, and Denbigh in North Wales - had to shut because the fairways and greens were buried by snow.
Temperatures dipped below freezing across the board overnight and are expected to remain in single figures for most of Wednesday.
Forecasters said a deep area of low pressure was centred over the UK, bringing with it the potential to drive showers and produce long spells of wet and changeable weather .
Met Office meteorologist Mark Wilson said: "In the north of the UK there will be more persistent rain and hill snow today, particularly on higher ground in southern Scotland and northern England.
"There is a weather warning in force in those areas for until 10 o'clock.
"There could be some snow to lower levels, but essentially it's a high-ground feature and it could cause some localised disruption over high routes."
Parts of Cumbria, Northumberland and Durham were in the warning area in England, while north of the border it covered parts of Dumfries and Galloway, East and West Lothian, East Ayrshire and South Lanarkshire.
Up to (2ins) 5cm of snow could accumulate above 200m and up to 4ins (10cm) above 400m, the Met Office said.
The band of rain and hill snow will push eastwards through Wednesday, while Scotland and Northern Ireland are expected to see strong winds with coastal gales.
There will be sunshine and some rain for the southern and western parts, although showers are forecast to be heavy with hail and thunder mixed in.
Temperatures will remain on the cold side, with around 5C or 6C the maximum for many and 10C expected in the south-east.
Little change in the conditions is expected for Thursday, although the focus for most of the showers will be in the south-west of the UK.
Hill snow will persist across high areas in the north, while in the south-west some drier and brighter weather is expected to arrive.
When will it end?
There is an improving picture towards the end of the week, with brighter, drier and warmer conditions expected for many parts on Friday and into the weekend.
Next week, the greatest risk of showers likely to be across southern and some eastern areas, with many places dry, the Met Office said.
It will feel cold in the east with brisk winds, while the west will be warmer.
The weather will gradually become more settled towards the middle of the month.
But overnight frost will remain a risk.
