The public is being warned not to travel unless absolutely necessary, as parts of south Wales are given a red “extreme” snow warning.
Roads, buses, trains, ferries and flights have all been affected as blizzard conditions are anticipated due to Storm Emma.
Forecasters said 8in (20cm) of snow is likely across much of mid and south Wales on Thursday.
Travel has also been affected in north Wales with some roads shut due to snow.
The red warning across south-east Wales is in force until Friday at 02:00 GMT.
“The message from Welsh Government is to plan ahead, take care and not to travel unless absolutely necessary,” said Welsh Transport Secretary Ken Skates.
“If you have to get out – whether travelling by road, rail, foot, bike or flight – familiarise yourself with the latest official advice before travelling and make sure a friend, family member or neighbour knows where you are.”
Bus and train services across parts of the south Wales valley networks have been hit, while all ferry crossings between Wales and Ireland have been cancelled.
Arriva Train Wales warned passengers to travel “as early as possible” as many services were ending early in the afternoon.
Llanelli-based Owens Transport said it had 31 lorries stuck in snow in Scotland and the north east of England.
Council gritters across Wales have been working around the clock but many authorities have warned that only main routes will be treated.
Wales’ Chief Medical Officer Dr Frank Atherton said people needed to keep warm, check on neighbours and if they go out – take care on the roads or to wear sensible shoes.
“We’re not used to very cold weather in this country. People need to understand these messages, it’s really a matter of common sense but sometimes people do ignore those messages,” he said.
An amber snow warning covering all of mid and south Wales is also in force, with a yellow “be aware” risk for counties across north Wales.
- Closed: A470 Ffestiniog, Gwynedd, between B4391 Ffestiniog and A487 Gellilydan
- Closed: A542 Horseshoe Pass, Denbighshire – between A5104 Llandegla and B5103 Llangollen
- Closed: A44 Llanbadarn Road, Aberystwyth, shut in both directions between A487 Penglais Road and A470, Llangurig
- Blocked: A4067 Westbound, Powys, affected by snow between Cray and Ystradgynlais
Advice from Arriva Trains Wales is to travel “as early as possible”
- Arriva Trains Wales: Cardiff Valleys services operating a temporary timetable -many will end in the afternoon
- Arriva Trains Wales: Replacement bus service between Llanelli and Craven Arms
- Arriva Trains Wales: Replacement bus service between Swansea and Fishguard/Milford Haven, Pembroke Dock
- Arriva Trains Wales: Reduced service between Wrexham General and Bidston
- Arriva Trains Wales: Replacement service between Llandudno Junction and Blaenau Ffestiniog
- Arriva Trains Wales: Cancellations between Cardiff and Manchester Piccadilly
- Arriva Trains Wales: Last service eastbound from Machynlleth, Powys, to Shrewsbury will be the 15:30 Aberystwyth train
- Irish Ferries: All sailings cancelled on Holyhead and Dublin crossings
- Irish Ferries: All sailings cancelled on Pembroke-Rosslare crossings
- StenaLine: All sailings cancelled for Thursday on Holyhead-Dublin crossing
- StenaLine: 08:55 Superfast X Holyhead-Dublin cancelled on Friday
- StenaLine: Fishguard-Rosslare sailings cancelled on Thursday
- StenaLine: 13:10 Fishguard-Rosslare crossing cancelled on Friday
- Cardiff Bus suspended services from 18:00 GMT
- Stagecoach: Some Cwmbran, Blackwood/Caerphilly and Merthyr Tydfil depot services have been suspended
- First Cymru: Short notice cancellations likely
- Cardiff Airport: Flights to Scotland, Paris and Berlin have been cancelled or delayed. All Flybe flights after 15:00 cancelled, in addition to 14:05 Faro, Portugal service