The UK is braced for a new wave of bad weather after forecasters issued warnings of heavy snow in parts of England and Scotland.
The Met Office put amber "be prepared" alerts in place for south-east Scotland and the Shetland Islands.
Snow started falling on Wednesday evening in Central Scotland and the east of the country while Scottish Borders Council has opened its emergency planning centre in preparation.
About 3-6cm of snow was expected quite widely, with the possibility of more than 10cm on higher ground.
Yellow "be aware" warnings were also issued, covering south and central Scotland, northern England, Yorkshire and Humber and the East Midlands.
The warnings are valid until 9am on Thursday, with commuters warned of travel disruption in some areas.
In north-west England, the snowy weather will mainly affect the Pennines and Cumbria and is unlikely to approach cities, the Met Office said.
Thursday will also see snow reach higher ground in Lincolnshire and Birmingham, the spokeswoman added.
Police Scotland said officers received a number of reports of incidents on roads across the north east of the country on Wednesday and advised motorists to take care.
Inspector Jon Barron said: "Emergency services have responded to a number of collisions.
"While inquiries into the circumstances are ongoing I would like to urge motorists to be aware of road conditions in cold weather.
"Please plan ahead, check the weather forecast and, if you must travel, allow more time for your journey."
The plummeting temperatures have also prompted public health chiefs to warn the elderly to keep their homes warm and have the flu jab as forecasters predict the cold front is set to remain into the weekend, with Scotland and northern England bearing the brunt of the wintry weather.
John Lee, a forecaster at MeteoGroup, said: "There will be a widespread frost and minimum temperatures overnight could get as low as minus 4C (24.8F) or 5C (23F) in Scotland.
"There will be snow across southern Scotland and northern England, which could be quite heavy at times, especially during the night.
"Over the next few days temperatures are unlikely to get much higher than 5C (41F) or 6C (42.8F) pretty much anywhere and we are likely to see more widespread frost."
The cold snap is in sharp contrast to last month, which was both the wettest and warmest December on record, when temperatures averaged 7.9C (46.2F).
Andrew Proctor, director of advice and support at Asthma UK, said: "With very cold weather expected across much of the UK this week, particularly on Thursday, people with asthma need to take extra care.
"Cold air can have a severe impact on people with asthma. As many as three-quarters of people with asthma tell us it can trigger symptoms, making sensitive airways tighten up quickly and putting people at risk of a potentially life-threatening asthma attack.
"If you find cold weather makes your asthma worse, make sure you wrap up warm, carry your reliever inhaler, and know what to do if your symptoms get worse."