Parts of the UK could see up to 10cm of snow on Thursday, with temperatures expected to drop “well below freezing” overnight, forecasters have said.
Snow has swept across the south-west of England, parts of Yorkshire, the north-east and Scotland, with more expected throughout the day.
More than 30 schools in Cornwall are either closed for the day or opening late due to hazardous conditions.
The Met Office has issued snow and ice alerts for large areas of Scotland, England and Northern Ireland amid plummeting temperatures.
The national weather service has advised of the likelihood of people suffering slips and fall injuries in one of the first icy periods of the winter.
It is also advising of the chance of disruption to road, bus and rail networks – with ice patches forming on untreated roads, pavements and cycle paths.
One yellow warning – covering areas in north-east England, the East Midlands, the east of England, Yorkshire and Humber and parts of Scotland – will be active from 5pm on Thursday until 11am on Friday.
Another, affecting Cornwall, Devon, Dorset and Somerset, will be in place until 4pm on Thursday.
Met Office spokesman Oli Claydon said parts of Dartmoor could potentially see 5-10cm of snow throughout the day, with other areas of the South West seeing “more modest accumulations” of one to three centimetres.
Overnight there is expected to be widespread frost, with temperatures dropping to -8C in the rural south and -7C in rural parts of Wales.
Mr Claydon said: “The cold conditions are set to remain for the remainder of this week and into the weekend. For those inland it will remain dry, crisp and cold but showers will continue along the east, becoming more north into the weekend.”
In County Durham, police said snowy conditions had led to some crashes on the roads.
Durham Constabulary said: “There has been the first main snowfall of the winter across the force area which has led to roads being covered in snow.
“We have already had collisions reported due to the weather. Please be careful if you need to drive this morning, drive to the conditions and allow extra time for your journeys.”
Yorkshire saw its first snowfall in the North Yorkshire hills earlier in the week, but it was reported to have settled in Leeds, York and parts of Bradford on Thursday morning.
Network Rail said it had not seen any “significant disruption” as a result of the cold weather but advised passengers to check before they travel.
East Midlands railway said passengers should expect some short notice cancellations and delays of up to 45 minutes due to a shortage of trains after damage caused by ice on the Corby/London St Pancras route.