Liverpool Airport has temporarily closed after a "deluge" of snow.
A John Lennon Airport spokesman said four flights from Malta, Berlin and Bucharest had been diverted to Manchester Airport, while a fifth from the Isle of Man had returned to the island's airport.
He added: "We are currently closed. It is just while we are clearing the runway. We have had quite a deluge here."
Police have issued warnings for roads in the Midlands and North West because of snow and sleet.
Roads around Delamere/Frodsham looking quite treacherous due to weather, Please drive with care
Snow has forced Liverpool's John Lennon Airport to close. Five flights into the north west airport have so far been rerouted elsewhere to allow runways to be cleared, a spokesman said.
Snow has been falling in parts of North Wales, the North West and the Midlands, with a Met Office Level Three amber cold weather alert in place and a yellow warning of snow across a large swathe of the UK.
Public Health England urged people to keep an eye out for vulnerable friends and neighbours during the cold weather.
Dr Angie Bone, its head of extreme events, said:
We advise people to keep active in the home, have plenty of warm food and drinks and maintain indoor temperatures to at least 18C - particularly the older or very young, people with pre-existing health conditions, or who are not very mobile, as these groups can be particularly vulnerable to the ill-effects of cold.
Also take some time to think about how the bad weather may affect your friends, family and neighbours - it's important we all do what we can to protect those around us.
If you do need to go out, remember to wear lots of thin layers and shoes with a good, slip-resistant grip to prevent any accidental falls.
Temperatures could drop as low as -10C in some places at the start of next week as a cold snap hits a large swathe of central Britain.
The Met Office today upgraded its cold weather alert to Level 3 amber, the second highest, saying there was a 90 percent chance of severe cold, ice or snow in parts of England between this afternoon and New Year's Eve.
The Met Office also said an area including Northern Ireland, Wales, the Midlands, East Anglia, the North West, Yorkshire and as far south east as London and Kent has been put on a separate yellow alert for snow.
A Met Office spokesman said that central and eastern Wales and the West Midlands were most likely to see snow.
Some significant snow accumulations are possible, especially on higher ground. Strong winds will develop in places for a time, exacerbating the chill.
Up to 10cm of snow could hit parts of Britain today as forecasters predict a cold snap in the lead-up to the New Year.Read the full story ›
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Parts of the northern Pennines are under a blanket of snow after the Met Office issued an amber warning for much of the Scottish Highlands and northern England.
The Met Office has issued a yellow warning for snow for much of the Scottish Highlands and northern England for Sunday and Monday.
Strong wind is expected on both days in Orjney, Shetland, the Highlands and Strathclyde, as well as heavy rain in southern England on Sunday.
The Niagara Falls on the US-Canada border could as well be in the Arctic this week after temperatures plummeted to record lows across the continent.