The UK is braced for more bad weather after forecasters issued warnings of overnight snow in parts of Scotland and England.
The Met Office put amber “be prepared” alerts in place for south-east Scotland and the Shetland Islands.
About three to six centimetres 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 from 7pm on Wednesday until 9am on Thursday, with commuters warned of travel disruption in some areas.
Police Scotland said officers had received a number of reports of incidents on roads across the north-east of the country on Wednesday morning and have advised motorists to drive to the conditions.
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.”
Scotland’s transport minister Derek Mackay said the public should check their travel operator’s website before they leave and be mindful of the conditions.
He said: “We have more gritters available across the trunk roads this year than ever before and these will be out with patrols across the day and night.
“There is plenty of salt available and the winter control rooms are monitoring conditions 24/7 to ensure that the fleet is treating and patrolling where required.”
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.”