Cars were abandoned and shops and schools closed because of the snow
Grit supplies are running low in many councils across Wales as more warnings of snow and icy conditions are forecast.
An all-Wales severe weather warning remained in place after sub-zero temperatures left roads icy overnight.
More than 300 schools were closed due to the bad weather.
The Welsh Ambulance Service warned it was having difficulty attending calls in north Wales and urged people only to dial 999 in a genuine emergency.
The service's communication manager Richard Timothy said the "exceptionally bad weather" was causing problems to ambulances on the road.
"If you need advice, please call the NHS Direct Wales line on 0845 46 47.
The cold spell is now putting gritting supplies under pressure, say councils
"Unfortunately, it is likely that patients waiting a response to a genuine 999 emergency call will experience delays, however the ambulance service will make every effort to attend calls as soon as possible," he added.
Ysbyty Glan Clwyd in Rhyl has cancelled all clinic appointments and all elective surgery for Wednesday due to the state of the roads around the hospital and because ambulances cannot guarantee they can bring patients to and from the site.
Meanwhile, workers at Airbus in Broughton were sent home and employees working the nightshift on Tuesday were advised to stay away because of the poor weather conditions.
The company said it would be open for "business as usual" on Wednesday.
The assembly government said it would free up road salt from its reserves to help local authorities running low.
The Welsh Local Government Association (WLGA) said some councils had only two to three days of gritting supplies left.
Police in north Wales continued to advise people to travel only if it was "absolutely essential".
The A55 in north Wales was described as treacherous earlier in the day and roads leading to Anglesey, Gwynedd, parts of Conwy, Denbighshire, North Flintshire and Mold proved impassable on Tuesday afternoon.
The Met Office is warning of heavy snowfall overnight in south east Wales, advising that 5-10cm (2-4in) is expected widely, with locally 10-15cm (4-6in) in Newport and Monmouthshire.
Gritting bin stolen
There is a moderate risk of more than 25cm (10in) of snow in a few places.
The WLGA said councils were helping each other out with supplies of gritting and salt although the "unprecedented scale of continuous salting and gritting" meant that main routes had to be given priority.
Chief executive Steve Thomas said: "Despite some media reports, there are no substantial reserves of salt in any parts of Wales and councils are largely reliant on deliveries from the Salt Union plant at Winsford in Cheshire.
"This plant is working at capacity but with the cold spell looking set to continue the reality is that there could be problems in matching supply with demand over the forthcoming period."
Deputy First Minister Ieuan Wyn Jones said the assembly government fully understood the pressures local authorities were under due to the severe weather.
He added: "We will do what we can to assist those who require additional stocks of salt on a priority basis, even though the government's responsibility is to maintain the trunk road network."
In Powys, the county council warned that its reserves of road salt were "critically low" and could run out if the severe weather continued.
The council said it normally carried stocks of about 14,000 tonnes of salt spread throughout 11 depots but had increased this amount.
However a spokesman said they had already used 13,000 tonnes in December, compared with an average of 5,000 tonnes.
In Swansea, highways officials criticised "selfish individuals" who arrived in vans to empty grit bins of minutes after they were filled up with salt.
Meanwhile, Flintshire council said a grit bin was stolen in Buckley. It was replaced and then the salt was stolen.
Coastguard four-wheel drive vehicles were brought in to help police and ambulance crews in north Wales and bus services cancelled in Denbighshire.
Ceredigion council reported its social services department was struggling to provide its usual home assistance services because of staff shortages caused by the disruption on the roads.
Day centres for older people were all closed on Tuedsay and some meals on wheels deliveries were affected..
Flights between Anglesey and Cardiff have been cancelled for Wednesday morning, with a decision on afternoon flights to be made in the morning, Highland Airways announced.
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