Snow and ice has gripped parts of the UK as a cold snap dubbed the "mini beast from the east" sweeps in.
Parts of eastern England and Scotland have already seen snow, with more expected in the Midlands and Wales.
More than 100 flights to and from Heathrow Airport have been cancelled and drivers are warned to take care.
Amber warnings of a possible risk to life affect north-west England, Yorkshire, the Midlands, London and south-east England from the afternoon.
Met Office yellow "be aware" warnings are also in place across much of the UK until Sunday.
Some 1-3cm of snow is expected across large parts of the UK on Saturday, while 5-10cm could fall in the areas with amber warnings and up to 15cm on hills.
The lowest temperatures were recorded near Carter Bar on the Scotland-England border, at -2.6C in the early hours.
Temperatures are likely to drop to around freezing and gusts of up to 70mph are expected in northern England and parts of Wales.
The Met Office said: "Travel delays on roads are likely, stranding some vehicles and passengers. And some delays and cancellations to rail and air travel are likely."
Strong winds also mean it could feel as low as -7C or -8C for some, forecasters said.
The cancellations at Heathrow mostly affect short-haul routes, although BA services to New York and Chicago have been disrupted.
A BA spokesman said: "During cold weather conditions aircraft have to be de-iced prior to departure to ensure that they are safe, and additional measures are being taken to ensure the safety of our operation is maintained at all times."