Cold weather has intensified across the UK, with more snow forecast, and overnight temperatures of -10C (14F) predicted in parts of the country.
Amber warnings for snow are in place, covering parts of Scotland, northern England, the East Midlands, the east and south-east of England and London.
The Met Office warned that travel disruption was likely on Wednesday.
On Tuesday four people died, hundreds of schools were closed and flights cancelled as heavy snow hit the UK.
The Met Office said up to 15cm (6 inches) of snow was expected to fall in parts of the East Midlands, the east and south-east of England and London.
The amber warning – meaning a possible risk to life and property – is in force between 00:30 and 10:00 GMT.
The Met Office said that delays to rail and air travel were also likely and some rural communities could be cut off.
Up to 40cm (15in) of snow could fall in northern England and Scotland, between Wednesday morning and 18:00 on Thursday, the Met Office warned.
"Strong winds will lead to drifting of snow and severe wind chill, while lightning could be an additional hazard, particularly near coasts."
A less-severe yellow warning for snow is in place for north-west England, Northern Ireland, south-west England and the West Midlands until 23:55.
Among the likely disruption on Wednesday:
- National Rail has warned train passengers that disruption to journeys could continue on Wednesday into Thursday and advise checking before travelling
- British Airways has said flights were likely to be disrupted throughout the week. For "several hours during the worst of the weather" on Wednesday it will proactively reduce flight schedules at Heathrow Airport.
- Norwich Airport confirmed it had closed on Tuesday evening
- Part of the A1 in Cambridgeshire is shut in both directions, between the A1M junction 17 and the A6121 at Tinwell
- Highways England said the A66 in Durham is closed between the A1M and the A685 and the A59 in North Yorkshire is closed westbound after the A61 between Harrogate and Skipton
- Dozens of schools in Scotland will remain closed, including all schools in East Renfrewshire, East Dunbartonshire, Fife, Stirling and Fulbrick
The UK is experiencing what is expected to be the coldest week of the winter.
On Tuesday three people died following a crash in Lincolnshire while one man died in a crash in Cambridgeshire, amid warnings of treacherous conditions on roads.
Meanwhile, 17 vehicles were involved in a crash on the A120, in Essex.
Scotland's transport minister has warned of potentially "extreme" weather conditions later this week.
Humza Yousaf has said said the amber warnings in force for many areas for Wednesday and Thursday could be upgraded to red.
In Northumbria, a major incident was declared by police on Tuesday after more than 500 homes were left without power in Cowgate, Newcastle, following an underground electrical fire.
Power was later restored to the area.
Weather warnings are expected to be in place until the weekend.
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