Motorists have been told to only drive if necessary in areas covered by the Met Office's amber weather warnings
These alerts are now in force across the UK - with heavy snow expected in a stretch from Stoke-on-Trent to Durham, as well as North Wales and some of Northern Ireland
Significant disruption to transport, power lines and phone network coverage is likely in those places
Parts of central and northern England could see up to 40cm (16in) of snow overnight
The UK recorded its coldest March night since 2010 last night, with -16C (3F) in the Scottish Highlands
Hundreds of schools have been shut in Wales, and more than 250 schools are closed across the West Midlands region
Gem O'Reilly
Live reporter
Weather watchers in the UK have sent their photos into BBC Breakfast.
From Wales to South Gloucestershire, blankets of snow can be seen across the country.
A wintry landscape in the Gower in south-west Wales
Enjoying the snow in South Gloucestershire
Surrey saw its fair share of snow overnight
Snowy rooftops in the seaside town of Whitby, in Yorkshire
Several schools across the UK are closed today due to the severe weather.
If you live in England or Wales, you can check if your child’s school is closed on your local council website via this link here., external
Image source, Getty ImagesThe scene this morning in Blackwood, Wales
More than 100 schools across Wales have closed due to snow.
These include 65 in Caerphilly, 43 in Rhondda Cynon Taf, four in Bridgend and 25 in Merthyr Tydfil.
Seven others in Newport have delayed their opening time to 10:00, to let snow be cleared.
Yellow snow and ice warnings are in place across south, mid and west Wales.
Image source, .Many of you will be looking out on snowy landscapes today, and we would love to see what the weather is like where you are.
You can send us your photos via the Get Involved button at the top of the page or by emailing us at haveyoursay@bbc.co.uk
Overnight temperatures plummeted to -14.6C in the hamlet of Altnaharra in Scotland, making it the coldest night of the year so far in the UK.
Temperatures also dropped to lows of -8C in the north of England.
In the north of Scotland, temperatures will stay below freezing over the course of Wednesday.
The conditions, which have been attributed to the Arctic blast, could bring more snow and ice throughout the UK.
The Met Office's chief meteorologist, Matthew Lehnert, said the weather "could cut off rural communities in the north and impact travel over the next few days".
Marita Moloney
Live reporter
With weather warnings in place for parts of the UK, you've been sending in your photos to BBC Weather Watchers since early this morning.
Here’s a selection so far:
Image source, BBC Weather Watchers/n_dee_sThere was enough in Rhiwbina, Cardiff, to make a snowman this morning
Image source, BBC Weather Watchers/Lesley SPeople in Four Marks, Hampshire, have woken up to a heavy deluge of snow today
Image source, BBC Weather Watchers/AngelaJA scene you don't see every day in Headington, Oxfordshire - a local landmark in a dusting of snow
Image source, BBC Weather Watchers/iscawatchCaerleon in Newport also saw heavy snowfall, as seen here on some train tracks
Image source, BBC Weather Watchers/PuffinThis garden in Norton Malreward, north east Somerset, was completely covered overnight
In addition to the Met Office warnings, a level three cold alert has been issued by the UK Health Security Agency (UKHSA) for the whole of England, which is likely to be reviewed in coming days.
Dr Agostinho Sousa, the agency's head of extreme events and health protection, advised people to check on vulnerable relatives, adding that pensioners or anyone with an underlying health condition should heat their home to at least 18C (64F).
Who's most at risk from cold weather?
Some people are more vulnerable to the effects of cold weather. This includes:
Image source, PA MediaMotorists are also urged to be extra cautious on the roads during the cold weather.
National Highways has issued a severe weather alert for snow in the south of England and urged people to consider if their journeys are necessary.
Dale Hipkiss, national network manager at National Highways, urged people to pack extra provisions in vehicles in case they become stranded.
"Keeping a kit of essential items like a torch and warm clothes, in your vehicle, can be vital in case you and your passengers become stranded in winter," he said.
"Freezing conditions bring so many hazards, such as snow and ice, and take every possible step to understand your journey in advance and allow lots of extra time when travelling to prepare for the unexpected."
Image source, Getty ImagesYellow weather warnings for snow and ice are in place in the south and east of England, south Wales, Northern Ireland and Scotland until Thursday morning.
The Met Office said further warnings, or updates to the current warnings, were "very likely".
The bitter conditions will persist until the weekend, with the conditions expected to worsen further north later in week.
The Met Office’s chief meteorologist, Matthew Lehnert, said the weather could cut off rural communities in the north and impact travel over the next few days across southern England and south Wales.
"Snow, ice and low temperatures are the main themes of this week's forecast, with the UK under an Arctic maritime air mass,” he said.
"The focus for the snow moves to southern England and South Wales tomorrow and some may wake up to a few centimetres of snow, with the south coast and far south-west likely to see a mix of rain and sleet. Further snow and hail showers are also expected along northern coasts, especially in northern Scotland."
Nathan Williams
Live reporter
Good morning and welcome to our live coverage as a cold snap from the Arctic sweeps across the UK.
Several national severe warnings for snow and ice have been issued by the Met Office, with more likely on the way in the coming days.
Further sleet and snow is expected across southern England and south Wales today, while scattered snow and hail showers will impact Scotland's northern coasts.
Some commuters are facing disruption, with the Met Office warning power cuts are also likely.
I’m joined by my colleagues Marita Moloney and Gem O’Reilly this morning, so stay with us as we bring you the latest updates on the cold snap.