A snow-bound vehicle in the Preseli hills area of north Pembrokeshire
Another band of heavy snow is moving across west and south Wales as councils battle to get enough grit to make roads safe for traffic and pedestrians.
Fresh snowfall started in Pembrokeshire about lunchtime on Tuesday and spread east within a couple of hours.
First Cymru bus services have been suspended in Swansea, Swansea Valley and Maesteg because of the weather.
Meanwhile, councils across Wales have had to resort to ration salt for road gritting as the freeze continues.
First Minister Carwyn Jones said extra gritting salt is expected to arrive by the end of the week.
Derek Brockway, BBC Wales weather forecaster
It looks like the heaviest snow will be in south, east and mid Wales - typically 5-10cm (2-4in) but possibly 15-20cm (6-8in) in the south Wales valleys.
There could be 25cm (10in) on the Brecon Beacons with bigger drifts and blizzard conditions.
Cardiff and Newport could have a fair covering - a few centimetres - as well.
On Tuesday night, the snow moves into mid and north Wales, generally lighter but moderate falls likely on the hills and the Denbigh Moors.
The snow eases off on Wednesday with the prospect of turning a bit milder over the weekend.
He said a "substantial amount" was on order from the UK government which would go to priority areas, while he encouraged councils to share stocks.
Evening classes were cancelled in Bridgend and Swansea colleges and the Bridgend Designer Outlet closed early.
First Cymru's website was reporting services across Swansea, Swansea Valley and Maesteg were suspended from 1930 GMT on Tuesday for the evening because access to the bus depot was becoming dangerous.
Services in Carmarthenshire are running via main roads only, while services in Neath Port Talbot and Bridgend were being curtailed.
Tuesday's fresh snow has not just been falling on the high ground as forecast, but it has been heavier in some places than others.
North Pembrokeshire has had particularly heavy snowfall, making the situation even worse in places near Crymych, Fishguard, St David's and Newgale, and causing several roads to be closed.
This snow is forecast to continue until Wednesday morning
Between 5-10cm (2-4in) of snow is forecast from Tuesday evening in south, mid and east Wales, with more possible on higher ground and valley areas.
In Pembrokeshire, gritting lorries are going to be patrolling all the primary routes all night and the council said refuse collections and the situation with schools would be decided in the morning.
Meanwhile in Powys, salt depots have had to increase security to prevent people helping themselves to supplies.
Andrew Jones, a council highways manager at Powys County Council said: "We are having to almost police our depots to stop people coming in.
Driving became particularly difficult for some as the snow returned
"We are keeping the gates closed and people have been turned away after they have driven in and started helping themselves.
The council had just under 1,000 tonnes of salt left and said that would normally last between five and six days. However, Mr Jones said with further heavy snow expected today it could only last two and a half days.
Torfaen council said it only had enough salt to last until Wednesday and still has to receive orders it made before Christmas.
A spokesperson said: "Salt levels currently stand at approximately 390 tonnes, which based on current use and predicted weather conditions should be enough to deal with the forecast snow tonight and tomorrow but salt resources will then reach critical levels.
"The council grit barns were fully stocked before Christmas and have yet to receive two orders made prior to Christmas."
Flintshire council has warned that its salt stock levels are "critically low" and staff are reporting daily to the government team who are allocating salt deliveries on a priority basis.
Wrexham council said it has five days of salt left if treating roads continues at the present rate.
Denbighshire council said grit stocks were "very low". A delivery of 160 tonnes has been promised but the council does not yet know when it will arrive.
Around 40 schools in Wales were partially or fully closed on Tuesday, but exams for GCSE and A-level pupils were guaranteed to go ahead. So far, only a handful of school closures are in place across Wales for Wednesday.
Councils have been working to ensure the exams can take place after examining bodies ruled out postponing them because of the snow and ice.
School closures in Wales on Wednesday
Welsh Water said it was experiencing three times more calls than usual from customers reporting burst pipes and leaking water mains caused by the cold weather.
Cardiff City's rescheduled FA Cup tie at Bristol City on Tuesday evening is going ahead, according to the host club.