Snow has caused travel disruption in parts of the UK, as temperatures plummeted overnight.
Police warned drivers to take extra care after wintry conditions led to a series of accidents on the M20 motorway in south-east England.
Yellow weather warnings for snow and ice are in place for large parts of the country for the rest of the week.
Forecasters said it was expected to be one of the coldest weeks of the winter so far.
A temperature of -5.7C was recorded in Katesbridge in Northern Ireland overnight.
Kent Police said “heavy snowfall” had affected the M20 near Maidstone and conditions were poor on other roads.
Officers advised drivers to stay in their vehicle with the engine running if they get stuck in snow.
The Met Office has warned of icy patches on roads along the east coast, with potentially difficult driving conditions on Monday morning.
Up to 3cm of snow could fall inland, mainly over hills above 100m high, while many people starting their working week with temperatures of between 0C and -2C.
“It’s going to be a cold week. Plenty of dry weather around, but many places will probably see some snow at some point – for a lot of us not really amounting to much at all,” Met Office forecaster Craig Snell said.
The Local Government Association said 1.5 million tonnes of salt had been was stockpiled.
“Gritters will be out treating thousands of miles of roads as the big chill bites, and councils will be keeping people up-to-date about weather forecasts, road conditions and gritting activity,” said transport spokesman councillor Martin Tett.
He encouraged people to look out for vulnerable and elderly neighbours, who may need assistance in the cold weather.
On Monday evening through to 15:00 GMT on Tuesday, there is a chance of snow and ice for the north of England, the north-west Midlands, Northern Ireland, Wales and Scotland.
“Quite a lot of the UK will see some snow as we head through Tuesday, but as it ventures into the Midlands, south-west England and eventually later in the day across south-east England, it’s just going to be a few flakes,” Mr Snell said.
“Don’t expect to build a snowman.”
The cold snap is expected to last until next weekend, with milder weather on the way the following week.