Heavy snow has struck across the north of England and Scotland, with an artic blast sending temperatures plunging to -10C.
Parts of the UK could see up to 20cm of snow while Met Office forecasters urge travellers to plan carefully.
A man walks a dog at Flaybrick Hill Cemetery as snow covers Birkenhead, northwest England
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The Met Office expects 10cm of snow in northern England and Wales, and up to 20cm in the Scottish Highlands.
The coldest temperature recorded this morning was -8.6C (16.5F) on Aonach Mòr in Scotland.
A Met Office alert for the North of Scotland has been extended from midnight to reach Central Scotland and the north west of England on Tuesday.
Snow has fallen across parts of Manchester, Liverpool, Lancashire, Northern Ireland and Scotland.
Liverpool was among the cities worst hit by snow today as temperatures struggled to rise above 0C (32F).
Merseyside's roads policing unit said it was dealing with "a number of incidents" on the roads, including a HGV stuck on the M57 southbound.
While Lancashire Police say there have been an "influx of road traffic collisions" in the area.
Parts of the UK could see up to 20cm of snow while Met Office forecasters urge travellers to plan carefully
More than 100 schools across Aberdeenshire, Moray and Shetland are closed today amid heavy snow and ice.
Ferries and flights have also been disrupted after 8cm fell overnight in Aberdeen.
At least 36 schools across Merseyside are closed due to "hazardous" conditions.
Five schools in Greater Manchester have shut their doors due to the "severe weather conditions".
In Lancashire, 10 schools are closed as snow hits the borough - and more is on the way.
Six schools in Northern Ireland are shut while a yellow weather warning remains in place.
Yellow warnings for snow and ice cover large swathes of Britain until Thursday
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Around 200 schools across Aberdeenshire, Moray and Shetland are closed today amid heavy snow and ice
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Met Office forecaster Craig Snell suggested there could be a "persistent band of snow" over three to six hours.
He said: "In the early hours of the morning, we’re looking at temperatures getting down to -12C in a few spots, Tuesday night possibly down to -15C.
"So certainly a very cold spell into Wednesday."
It comes as some weather analysts have suggested that the nation might encounter its most severe snowstorm in 14 years.
Low overnight temperatures bring a layer of snow to the residents of Cheshire
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However, the Met Office is more cautious in its forecasts but added that there is still uncertainty arising from various weather systems.
Temperatures are around 5C to 6C lower than usual for this time of year, and the Met Office also warned that strong winds could result in drifting of lying snow in places.
Our reporter Sophie Reaper, who has captured snowy scenes in Wigan said: "A @metoffice yellow warning for ice and snow is in place here in the North West today. If you’re out and about, make sure you’re talking all necessary precautions!"
A man pulls two children through the snow on a sledge at Camp Hill in Woolton, Liverpool.
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Snow covered roads in Keswick in Cumbria as snow continues to fall
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Following the lashing of snow across Scotland, Transport Scotland said that it had "well-established plans" in place to minimise disruption.
Head of transport resilience, Stein Connelly said a multi-agency response team would be working to co-ordinate resources.
He said: "This cold snap is already causing difficult driving conditions, with further severe impacts anticipated on Tuesday as part of the existing warnings.
"It's important that anyone that has to travel during the warning period plans their journey in advance and allows extra time.
Some weather analysts have suggested that the nation might encounter its most severe snowstorm in 14 years
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A person walks through the snow on Knutsford Heath in Cheshire as temperatures plunge to sub-zero
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"If you have to travel, please drive to the conditions. There may also be disruption on other modes of transport, so please check before setting off."
A Met Office spokesperson said: "Snow showers will continue to feed inland early on Tuesday morning across northern and western Scotland, parts of Wales and northwest England where 2-5 cm of snow is possible over a few hours in some places.
"During the day, an area of more organised rain, sleet and snow is likely to move east with further showers following.
"There is still some uncertainty in the track of more prolonged snow, and it is possible that at lower elevations across Wales and northern England, this could turn to rain for a time.
"However, there is a chance some places could see 5-10 cm perhaps 20 cm of snow, particularly across the northern half of Scotland and over higher ground elsewhere."