Rural roads were among the most difficult, if not impassable, while major routes were largely clear The Wales Ambulance Service has warned of potential “long delays” in responding to 999 calls, as more heavy snow is forecast for Monday.
It said people should ring 999 only in a life-threatening emergency, as treacherous road conditions put a strain on its transport.
Motorists are continuing to face severe icy conditions across Wales.
Drivers at a Cardiff Tesco complained they were stranded in its car park on Sunday for up to four hours.
Forecasters say south and west Wales will be hit by up to 10cm (4in) on Monday, with up to 20cm (8in) on high ground.
However, the Met Office said there was “considerable uncertainty” about the “extent and depth” of the snow and urged people to watch for updates.
Temperatures were forecast to drop as low as -15C (5F) in places overnight, creating more problems for people returning to work in the morning and for the school run in those counties whose schools are still open.
A number of schools in Carmarthenshire, Ceredigion, Gwynedd, Powys and Anglesey have already announced they will be shut on Monday.
“We would ask that you only contact 999 if absolutely necessary and only in the event of a life threatening emergency”
Wales Ambulance Service
People are advised to check the website of their local authority for details of school closures in their area.
Ceredigion councils said there would be no waste collections anywhere in the county on Monday.
Household bin collections are currently suspended in Cardiff. The council said it would resume collections as soon as it was safe to do so.
Many roads remained dangerous and a severe ice warning has been in place.
The ambulance service said the weather had brought difficulties in maintaining its normal service for routine patient transport.
It is said it expected many hospital clinics to be closed on Monday, so patients will not have to attend.
A spokesman said it would concentrate on patients identified by health boards as being at clinical risk, such as renal and cancer patients.
He said: “As a result, no other patients will be transported unless it is at the specific request of a hospital due to the urgent nature of the treatment needed.”
Shoppers at this Cardiff Tesco car park said they faced delays of up to four hours to get out He added: “With regard to the 999 ambulance service, we would ask that you only contact 999 if absolutely necessary and only in the event of a life threatening emergency.
“Please also be advised that there will potentially be long delays in emergency vehicles getting to patients.”
The icy road led to unhappy shoppers at the Tesco Extra store on Western Avenue, Cardiff.
Mother-of-three Sharon Matthews, from Thornhill, Cardiff, said she was stuck there for four hours on Sunday afternoon trying to get out after calling in for provisions, including cough mixture for her seven-year-old son, George, who was in the car with her.
Before being able to leave, she said: “We were hoping to get back by lunchtime. The air is getting a bit damp and we are turning the car on and off.”
Police said the delays were due to the amount of traffic at the site as people went out after a day when many had been stuck in.
Tesco has been asked to comment.
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