A fresh fall of snow is causing hazardous conditions and many accidents on Cornwall's roads.
Traffic standstills left up to 100 drivers stranded on the A39 at Devoran. A jackknifed lorry blocked one lane of Morlaix Avenue in Truro.
About 190 schools were closed. Many others that reopened in the morning closed again as snow falling on to freezing roads turned into ice.
All hospital outpatient clinics in the county have been cancelled.
The local economy is losing £10m a day according to businesses, as an estimated one tenth of the workforce stays at home.
Farmers are throwing away thousands of gallons of milk because lorries cannot make it down iced-up minor roads.
Hospitals are struggling to cope with an increase in accidents from people falling over on the ice and an outbreak of the winter vomiting bug.
Some ambulances were left stuck on the icy roads and coastguards from Falmouth used four-wheel drive vehicles to transport some patients.
The fresh snow has caused hazardous driving conditions
All outpatient clinics have also been cancelled at the Royal Cornwall, West Cornwall and St Michael's hospitals, as well as those at community and peripheral hospitals, because of weather and road conditions.
Health bosses said they were reviewing whether Friday's clinics would be held.
Road incidents have been reported across the county, with vehicles being involved in collisions or being stuck in ice.
Two school buses were stuck in the snow at Leedstown and Chiverton, causing long tailbacks.
In Truro, two buses and a lorry travelling towards Penair school became stranded at the top of St Clements Hill, blocking the road.
A tanker got stuck at traffic lights at the top of Tregolls Road on the way out of the city, causing major tailbacks.
The weather has been disastrous for businesses
Jeremy Filmer-Bennett, Devon and Cornwall Business Council
Vehicles were also left stuck at the top and bottom of Morlaix Avenue because of ice before the jackknifed lorry incident. Cars have also been abandoned on the road.
Cars were also abandoned at Woodcock Corner at Tresillian. The Trispen bypass is shut and the Probus bypass has been reported as being very icy.
First Great Western and South West Trains are running revised timetables and flights from Plymouth and Newquay airports have been disrupted.
Temperatures are expected to just creep above freezing in the county, with the forecast of more freezing weather and snow over the weekend.
Surfers at Fistral beach had to walk through snow
Hail showers are forecast for the Isles of Scilly on Thursday.
Cornwall Council said that highways staff carried out a full precautionary salting run on Cornwall's A and B roads from 0600 GMT on Thursday.
It added that 75 gangs were working across the county to treat footways in the main towns where possible and also refill salt and grit bins.
Jeremy Filmer-Bennett, chief executive of the Devon and Cornwall Business Council, told BBC News: "The weather has been disastrous for businesses.
"Losses of £10m a day is probably a conservative estimate.
"We have plenty of examples of businesses where staff cannot get in so it really is a major financial hit.
"And parents of children who cannot get into work because of childcare issues are customers and workers.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.