The first flakes of snow have started falling in Norfolk amid forecasts of sub-zero temperatures across the region this week.
The so-called 'Beast from the East' cold snap could force temperatures to plummet to -5C and there is a chance of 10 to 15 centimetres of snow on a 'widespread' scale.
There have been reports of snow fall across the region this morning and a yellow weather warning for the white stuff will be in place from 2pm until 11.55pm on Wednesday.
Greater Anglia has also warned its services could be affected by the predicted sub-zero temperatures and snowfall.
A reduced service will start from 8pm tonight and services will end by 10pm to allow trains to return to return to depots and stations before the forecast snow storms start.
Hundreds of trains due to depart today and tomorrow have already be cancelled and these included services from Norwich to London Liverpool Street, Great Yarmouth, Lowestoft and Cambridge.
A limited service could then be enforced from 6am tomorrow until 10pm on Wednesday.
MORE: Check if your local school is open amid forecast snow
Dan Holley, a meteorologist at Weatherquest, based in Norwich, said: 'Every day this week there's pretty much a chance of some snow.
'But unlike in the past when it's been one event and then it's over, there will be various rounds of snow throughout the week.'
He said it made it difficult to pinpoint where exactly would get snow - and how much - but that, generally, most places would see two to five centimetres of snow by Wednesday lunchtime, with the coast potentially receiving more.
Snow will continue throughout today and on Tuesday there will be more showers, which will continue on and off until Wednesday lunch time, with temperatures hovering at sub-zero.
By Wednesday afternoon, things will become dry and cold, and Mr Holley said they were keeping a 'very close eye' on what happened on Thursday.
Health alerts issued
Health bosses have warned people to take extra care of those who may be vulnerable.
Public Health England's extreme events team has issued a health warning ahead of the cold snap.
Dr Thomas Waite, on the team, said: 'Cold temperatures, indoors and out, pose real health risks to many and every winter we know that thousands of people get ill and even die following exposure to cold conditions.
'As forecasters tell us [this] week temperatures will fall, it's critical that if you know anyone over 65, with young children or who has heart or lung conditions, that you keep an eye on them and think what help they may need. Staying warm by heating your home to at least 18°C can be crucial to stay well.'
Cold weather health alerts operate on a four-tier scale - ranging from one, 'winter preparedness', to four, 'national emergency'.
While the UK was on level two, over the weekend it was ramped up to a level three, 'cold weather action'.
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