Drivers are being warned they could face major disruption on Tuesday morning as heavy snowfall looks set to blanket Britain and cripple much of the country's travel network.
The Met Office said more than 20cm of the white stuff could settle by Wednesday as a wintry blast, dubbed the "Beast from the East", will cause temperatures to tumble, with the country potentially facing the coldest weather since 1991.
Amber warnings have been issued for snow showers on Tuesday morning, covering the South East and North East of England and the East Midlands.
Forecasters say up to 15cm could fall in just a few hours, with the warnings in place between 2am and midday.
A yellow warning is also in place for vast swaths of the UK for nearly 24 hours from just after midnight on Tuesday.
Met Office forecaster Marco Petagna said there would be some "quite treacherous driving conditions" due to the snow, as many make their way into work.
"Most people will have to travel, but if you don't have to travel - it is best to try to avoid if you can within those amber warnings," he said.
Schools could also be hit by closures due to the heavy snowfall, as school leaders said keeping staff and pupils safe should be a top priority.
Latest Met Office weather forecast
The fallout from the "Beast from the East" had already begun Monday, with commuters rushing home, shoppers stocking up with essentials and rail and air services cancelled as forecasters and operators warned of plummeting temperatures.
The Met Office has also put out a new warning as Storm Emma is due to hit the UK on Thursday and Friday, bringing heavy snow, blizzards and high winds.
"The Portuguese met service @ipma_pt have named #StormEmma, bringing strong winds to the Portuguese coast on Wednesday. Emma may then bring strong winds and heavy snow to parts of the UK during Thursday and Friday," the Met Office tweeted.
Some parts of the UK are forecast to feel colder than the Arctic Circle as freezing temperatures continue into the week ahead, and amber warnings of snow have been issued by the Met Office for north east, central and south eastern England on Tuesday, and eastern Scotland on Wednesday.
Although Sadiq Khan, the Mayor of London, and TfL promised they would do all they could to keep London moving, frustrated commuters still faced cancelled trains and huge delays Monday.
One commuter wrote: "Londoners who use trains to get to work: all of mine were cancelled this morning. If you don’t live on the underground network you might want to leave 30 mins earlier than usual."
Another said: "A few flakes of (barely visible) snow and my train is cancelled. So predictable."
A few snowflakes and every train is cancelled until at least 11 lol #englandweather— kimi �� (@kimitsuruu) February 26, 2018
**NEW** 26/02 Due to a problem currently under investigation at Bracknell, trains have to run at reduced speed on all lines. Train services running through this station may be cancelled, delayed or revised. Disruption is expected until 10:00 26/02.— SWR Help (@SW_Help) February 26, 2018
Network Rail said it will attach heaters and Nasa-grade insulation to points - the section of rail that moves to enable trains to switch between tracks - to prevent ice forming. Empty trains will also be run overnight in order to keep lines open where possible.
Even so Greater Anglia, which serves Norfolk, Suffolk and Essex, ended services early on Monday at 10pm and a string of cancellations was announced for Tuesday.
It is getting colder this week, with snow expected later today. We're working closely with @NetworkRailSE to keep the network open, but please check before you travel. #UKSnowpic.twitter.com/nb9NuuNmoL— Southeastern (@Se_Railway) February 26, 2018
London Underground services were also severely delayed during the rush hour as snow was sighted in Central London.
Shoppers around the UK and in Ireland reported long queues and empty shelves at supermarkets as panic buying set in.
A Met Office spokesperson said: "Travel delays on roads are likely, stranding some vehicles and passengers.
"Some delays and cancellations to rail and air travel are likely.
"There is a good chance that some rural communities could become cut off.
"Power cuts are likely and other services, such as mobile phones, may be affected."
The cold snap began to creep in over the weekend, with temperatures of minus 5C recorded in some parts of the country, which marked the lowest temperature in the week leading up to March 1, the first day of spring, since 1986.
The wind chill, which could see parts of the UK feeling as cold as minus 15C (5F), rivals the temperatures forecast for parts of northern Norway and Iceland.
Charlie Powell, a Met Office meteorologist, said: "The UK is on track for some really cold weather this week. It's not going to be record-breaking, but it'll be pretty exceptional - winds are going to make it feel minus 10C (14F) to minus 15C (5F) during the day.
"Winds are then going to strengthen (Tuesday) and we could see some easterly gales through the eastern Channel and east Anglia by the middle of the week.
"That's going to make it feel really cold, daytime temperatures on Wednesday and Thursday will be struggling to get above freezing for most of the country."
He added that growing indications suggested that there could be significant snowfall across southern England by Thursday evening.
"Unusually for Britain, the snow is going to be quite dry, so it will blow around and gather in drifts and we could see some blizzard conditions," he said.
"We don't want to scare people, but people should make sure they are prepared for some seriously cold weather."
Rome is under a blanket of snow as weather chaos hits Europe
Romans woke Monday to a rare snowfall, after an Arctic storm passing over much of Europe dumped enough snow to force schools to close and public transport to reduce services.
Rome's Mediterranean climate and proximity to the sea usually result in mild winters, such that restaurants often keep outdoor seating open even through the coldest months of the year. As a result, the Monday morning snowfall, though not huge in quantity, brought excited young Romans out for a rare snowball fight or walk in the slush.
Virginia Raggi, the city's mayor, signed an ordinance Sunday evening closing public schools as a precaution, and many private ones followed suit.
Elsewhere in much of northern and central Italy, the storm also closed schools and disrupted transport.
Moscow is also feeling the freeze; temperatures in Russia have dropped to this winter's low despite the approaching spring.
The Meteorological Office said on Monday the mercury in the Russian capital dropped to nearly minus 20C (minus 4F) on Sunday night, the coldest night this winter.
Meteorologists are forecasting unusually low temperatures for early March. Roman Vilfand, chief of the Russian Meteorological Office, told the Interfax news agency that Muscovites should brace themselves for frosty weather in early March and could only "count on the warmth of the soul", not higher temperatures outside.
Moscow earlier this month saw what has been described as the strongest snowfall on record when more than a month's average of snow fell on the city, turning streets and yards into snowdrifts.