More than 100 schools in Scotland and over 30 in England have been closed due to an Arctic cold front set to sweep across the UK this week, which is also expected to cause travel chaos.
The UK Met Office has issued yellow warnings for snow and ice in Scotland, Northern Ireland, and parts of England and Wales, reports Xinhua news agency.
The freezing weather is expected to continue until Thursday.
Temperatures may drop to freezing lows of -15 degrees Celsius in parts of Scotland, according to the forecaster.
"The UK is now in the grip of a cold plunge of Arctic air which has moved in from the north across the whole of the country," the national meteorological service said.
By the end of Friday, more than 40 cm of snow may be seen on high ground in north-west Scotland, as wintry weather continues, the Met Office has forecast.
Snow, sleet and rain are expected to continue blanketing northern parts of the UK, though there will be some sunshine.
Heavy frosts and freezing conditions are likely across virtually the entire country, with experts warning of treacherous pavements and roads.
Earlier on Tuesday, the Met Office posted on social media: "Tonight could be the coldest January night for 14 years with temperatures possibly falling as low as -15C in snow covered parts of Scotland".
Meanwhile, the National Highways issued a severe weather alert for snow affecting the North West, warning of "possible travel delays on roads with some stranded vehicles and passengers".
A few rail operators also urged travelers to "be careful as platforms and pathways may be slippery", and to pay close attention to the latest service information.
An amber cold-health alert issued by the UK Health Security Agency (UKHSA) is currently in place for the whole of England until midday Friday.
"The temperatures we will see leading into the week ahead can rapidly have a serious impact on the health of those over the age of 65, and those with pre-existing health conditions, as it increases the risk of heart attacks, strokes and chest infections," said Agostinho Sousa from UKHSA.
At around Tuesday night, there were also 20 flood warnings and 65 flood alerts in place in England.
The lowest temperature so far this winter was -12.5 degrees, in Altnaharra, in December 2023.
In January 2010, -22.3 degrees was recorded in the same Scottish Highlands hamlet.
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