A snow warning for parts of Wales is now at the highest red "extreme weather" level.
Storm Emma has caused travel chaos with more than 1,000 schools shut across Wales on Thursday.
It is the first red warning for snow in Wales since 2013.
The Met Office red alert covers the whole of south-east Wales until 02:00 GMT on Friday with counties across most of north Wales covered by a yellow "be aware" warning for snow.
Other parts of the UK are also facing major disruption due to the severe weather.
An amber "be prepared" warning covering mid and other parts of south Wales remains in place from 12:00 GMT until 08:00 on Friday.
The Welsh Government is urging people not to travel unless absolutely necessary and there are already disruptions to roads, buses, trains, ferries and flights.
A red warning is the most severe issued by the Met Office - it means people should take action now to keep themselves and others safe, with widespread damage, travel and power disruption and risk to life likely.
It covers Blaenau Gwent, Bridgend, Caerphilly, Cardiff, Merthyr Tydfil, Monmouthshire, Newport, Rhondda Cynon Taff, Torfaen and the Vale of Glamorgan.
The Met Office warned "widespread snow" and strong winds are expected to move north throughout Thursday afternoon and evening.
Higher ground could see as much as 20in (50cm) of snow and some places could experience a "significant" build up of ice overnight into Friday.
Public Health Wales has urged people to look out for friends and family who may be vulnerable to the cold.
Meanwhile, two Newport nightclubs, Courtyard and Blind Tiger, have opened their doors to the homeless due to the weather with 15 people so far taking up the offer of free food and airbeds.
Health services have also been affected, with Aneurin Bevan health board cancelling all outpatient appointments on Thursday afternoon and for Friday. Its hospital sites in Newport, Abergavenny and Ebbw Vale at the heart of the red-threat region.
Abertawe Bro Morgannwg health board said it would be cancelling some appointments on Thursday and Friday and was contacting patients directly, while Cwm Taf health board has halted all outpatient clinics on Thursday afternoon.
Cardiff's Velindre Cancer Centre has also warned patients not to attend appointments on Thursday or Friday - unless staff contact them.
Powys Teaching Health Board said some services were "unfortunately being cancelled due to the weather and travel conditions".
Every school has been closed in Blaenau Gwent, Neath Port Talbot, Cardiff, Vale of Glamorgan, Caerphilly, Bridgend and Ceredigion.
All campuses at Swansea University, the University of South Wales, Coleg Menai and Coleg Gwent have been shut for the day while all schools in Pembrokeshire closed at lunchtime and will not reopen until Monday.
The weather has forced organisers to cancel the annual St David's Day parade in Cardiff, along with the national service due to be led by the Archbishop of Wales.
Work at the Welsh Assembly in Cardiff Bay is ending for the day while committee meetings due to take place have been cancelled or are wrapping up early.
Councils have also urged residents to check their websites for updates on road conditions, recycling collections and school closures.
Elderly residents have been told to "prepare but not panic" by Age Cymru. The charity has advised older people to dress warmly if they go outside, or to make sure they keep their homes heated and move around if they do become housebound for a few days.
The Met Office has also issued a yellow "be aware" warning of snow and ice from 00:05 on Friday until 23:55 on Saturday with between 2-4in (5-10cm) anticipated to fall.
It follows freezing temperatures and snowfall across Wales on Wednesday.
School closure information