Shetland and parts of eastern Scotland have woken up to a white Christmas, the Met Office confirmed.
As of 7am on Christmas Day, the weather agency said there had been snowfall, with more forecast for later in the day in the southern Highlands.
Aboyne in Aberdeenshire and Strathallan in Perthshire were found to have encountered some snowfall overnight.
On Twitter, the Met Office said: “We’ve already seen some #snow in Shetland, parts of eastern Scotland.”
A tweet from the Met Office also noted that snow had been seen in the Yorkshire Dales via traffic cameras.
A Met Office spokesperson said: “We have seen snowfall through the early hours of Christmas Day, though there has not been any significant snowfall since 5am this morning.
“Up until then we saw snowfall across Aberdeenshire, Perthshire and Shetland.
“We have seen snowfall on Christmas Day, so it is officially a white Christmas.”
No further significant snow is expected until after midnight, the spokesperson added.
Moving into Boxing Day, more snow is expected in parts of central and southern Scotland and the north-west of England, with the Met Office issuing a yellow weather warning.
Coming into effect just after midnight, the warning will last until noon, according to the agency.
A combination of strong winds and snow on higher ground is expected to disrupt travel.
Roads and railways could be impacted, with the possibility of power outages.
Elsewhere, a Christmas weather warning has been issued for rain in Northern Ireland.
Due to be in effect from 3pm on Saturday to 9am the following day, parts of County Down and County Armagh can expect heavy downpours.
The rain could also result in travel disruption and the Met Office said “flooding of a few homes and businesses is likely”.
London will see temperatures of around 7C (44.6F) dropping to 6C (42.8F) around noon, with a chance of rain in the evening, while Manchester will be colder, dropping from 4C (39.2F) to 3C (37.4F) later in the day, with a likelihood of rain after 10pm.
Edinburgh will fluctuate between 2C (35.6F) and 3C with no rain expected, while Belfast is likely to see rain all day and temperatures of 6C.
Forecasters say Cardiff will be around 8C (46.4F) or 9C (48.2F) on Christmas Day, but with rain expected throughout.