Heavy snow is causing disruption across parts of Scotland, with drivers stranded in long queues on a motorway.
Mountain rescue teams have been sent to help stranded drivers on the M74 after wintry conditions led to closures at Millbank and Beattock.
Traffic Scotland said gritters were clearing routes, as driver in Dumfries and Galloway were warned not to travel.
Snow has also caused problems in Northern Ireland, forcing schools to close and disrupting public transport.
An amber Met Office warning for snow and ice is in place in south-west Scotland, extending to parts of the central belt, and parts of Northern Ireland until 08:00 on Wednesday.
Forecasters warn of “heavy squally showers of snow” which may cause power cuts and disruption on the roads, with up to 25cm (9.8ins) of snow possible on high ground, and up to 10cm (4ins) at lower levels.
Much of England and Wales is covered by a less severe yellow warning for snow and ice on Wednesday and for snow and strong winds in some places until the end of the week.
Police in Dumfries and Galloway warned against “all but essential travel” on Tuesday night.
Dumfries & Galloway Virtual Operations Support Team – which was set-up to respond the weather issues in the region – said: “We have tasked Moffat Mountain Rescue Team to attend and check on those drivers stuck in their vehicles.
“We are working to clear the stuck vehicles and clear the crashes.
“Please remain in your vehicle and signal the mountain rescue team or police if you need any help or contact us via 999.”
Earlier, motorist Nigel Cliff, who was heading south and was caught up in the tailbacks on the M74, told BBC Scotland: “It’s pretty rough.”
“It’s snowing again now so it is probably only going to get worse. There are cars and lorries just sitting here – nothing moving.”
Mr Cliff said he was prepared for the conditions: “I’ve got food. I’ve got big thick coats, big thick socks. My wife always makes sure I’ve got everything in the car.”
Scottish Fire and Rescue’s station manager in Dumfries and Galloway said motorists had been driving “too close behind me” on his way to a crash, despite “blizzard conditions”.
#SFRS Thornhill and Dumfries attend RTC in blizzard conditions at Auldgirth. Whilst on route to incident drivers still driving too close behind me. No possible way for them to stop. Drivers reminded to slow down and take care @scotfire_DG@DumfriesGPolicepic.twitter.com/JBhD0UqgyP
— Ian Anderson (@iananderson110) January 16, 2018
End of Twitter post by @iananderson110
Traffic Scotland said late on Tuesday evening that traffic was moving slowly again at junction 12 southbound and between junctions 14 and 15 northbound where there had been earlier closures.
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On the Isle of Skye, the main road – the A87 – was blocked for several hours in both directions by a jack-knifed lorry.
The closure meant two school buses with pupils who had been stuck for hours had to return Portree High. The school said they would be put in temporary accommodation for the night.
On Tuesday evening, Scotland’s Transport Minister Humza Yousaf tweeted that a number of HGVs had “lost traction with challenging weather impacting on M74”.
He added: “Necessary to close the junction to get additional gritters and equipment to the scene.”
Seems a number of HGVs have lost traction with challenging weather impacting on M74. Long queues and delays. Necessary to close the junction to get additional gritters and equipment to the scene https://t.co/Z4trUEcHy2
— Humza Yousaf (@HumzaYousaf) January 16, 2018
End of Twitter post by @HumzaYousaf
Across Scotland more than 100 schools and nurseries were closed on Tuesday, with more than 10,000 pupils missing classes.
In the Highland council area, the weather affected 13 secondary schools, 53 primaries, two special schools and 26 nurseries. About 8,900 pupils had an unexpected day off classes.
Dumfries and Galloway Council said 20 schools were closed due to weather problems or heating failures. Some schools also closed in the East Ayrshire and Stirling Council areas.
In North Lanarkshire, all prelim exams for secondary pupils were postponed due to transport problems and all cafes in council leisure and culture buildings were shut.
South Lanarkshire Council closed 18 schools and nurseries throughout the day.