Up to four inches (10cm) of snow is expected to fall in parts of England and Wales overnight raising fears of widespread disruption to the roads and railways.
Forecasters said the freezing weather was set to continue for the next few days, with temperatures expected to plummet to -8C (18F) over the weekend.
The cold spell has already led to a string of road accidents, with 100 reported in Cumbria alone today.
And charities have warned that elderly people are among the most vulnerable in the freezing conditions.
Age UK director general Michelle Mitchell said more than a third of over-65s fall each year, with snow and ice posing a particular risk.
She said: "Winter can be a dangerous time for older people particularly with the current plummeting temperatures.
"Low temperatures raise blood pressure which puts people at a greater risk of heart attacks and strokes as well as increasing the likelihood and severity of flu and other respiratory problems.
"During this period of cold weather, we would urge people to check on their older relatives or neighbours to ensure they are warm and have plenty of food.
"We would also encourage people to be good neighbours and clear pathways of snow and ice, if they are able to help older people stay safe."
A spokesman for the Association of Train Operating Companies (ATOC) said train companies were gearing up to deal with the bad weather, with Network Rail running empty 'ghost' trains and de-icer units to keep tracks and overhead cables free of snow and ice as far as possible.
He added: "The whole industry will be working hard to get people from A to B as quickly and reliably as possible."
Martin Young, chief forecaster at the Met Office, said: "We are expecting some snow across parts of the country overnight and into Friday.
"Whilst there is uncertainty about where the heaviest snow will be, we expect a covering of 1cm to 5cm of snow in many areas and possibly up to 10cm in the worst affected regions of perhaps the Midlands and south east Wales.
"As a result there could be some disruption to travel."
Chris Burton, forecaster at MeteoGroup, the weather division of the Press Association, said snow was forecast to fall in Yorkshire, the Midlands, central southern England, western parts of East Anglia and London.
He said: "Tomorrow, with cloudy skies, temperatures won't drop too low but it will be generally freezing across most of England with lows of -1C (30F) or -2C (28F).
"It will struggle to get above freezing in parts of East Anglia but it will get up to 1C (34F) or 2C (36F) in England."
He said London should expect more than an inch (2-3cm) of snow overnight, while the Midlands would get the heaviest covering.
Snow was already falling this evening in the East Midlands and Yorkshire.
Mr Burton added: "It will be a very cold night on Friday as the cloud will have cleared so it will get down to -7C (19F) or -8C (18F) in some parts."
A spokesman for Cumbria County Council warned that road conditions were expected to remain hazardous for the next 24 hours, describing the freezing rain falling on the ground as a "perfect storm".
She added: "Although air temperatures have risen above freezing in many places, ground temperatures remain below zero, causing the rain to freeze on the ground and create patches of black ice.
"Drivers are being urged to avoid travelling unless absolutely necessary."
Six vehicles also collided in freezing conditions on the Felling bypass in Gateshead, Tyneside, this morning and drivers were trapped after a crash in Gateshead at the junction of the A194 and the A1 southbound.
One man was taken to hospital after being knocked over a barrier as several vehicles collided in the ice on the Blaydon Highway flyover, Tyneside, at around 6.45am. His condition was said to be stable.
Meanwhile, it emerged that a man is thought to have drowned trying to rescue his dog from a freezing pond at the weekend.
Classic car enthusiast Tim Waddingham, 53, was pulled from a pond at Wildwood Golf and Country Club, in Horsham Road, Cranleigh, Surrey, at about 4pm on Sunday, a Surrey Police spokesman said.
Mr Waddingham's dog was found by the lake at the nine-acre course by members of the emergency services. A post-mortem examination showed his cause of death was drowning.
North West Ambulance Service said its control centres had answered almost 700 emergency calls since 8am today.
The emergency service had also responded to 187 incidents where patients had fallen.
A Network Rail spokesman added: "We are working closely with the forecasters and train operators to track the weather system across the country and put plans into action to run the best possible train service for passengers."