Police are urging people to stay in their cars to keep warm after around 20 cars were abandoned on Cornwall’s A39 dual carriageway amid heavy snow.

Devon and Cornwall Police issued the warning after videos showed cars slipping and sliding as they attempted to drive along one of the main roads in the area.

The South West appeared to be hardest hit by the cold snap as snow 12cm deep was measured on Bodmin Moor in Cornwall, according to the Met Office, and schools an airport were closed.

Earlier, an “intensive effort” was under way to help stranded motorists on the A30 in Cornwall.

At around 8.15pm on Thursday, the force tweeted: “We have further reports of vehicles stuck on the #A39 in #Cornwall due to snow.

“Please stay with your vehicle and keep as warm as possible. Gritter trucks are working their way inwards from Winnards Perch and Wadebridge to get to stranded drivers.”

Cornwall Council said it was having trouble clearing the road due to abandoned cars blocking the path.

Matt Argyle, 46, got stuck on the A30 eastbound just before Temple after returning from St Austell.

He told the Press Association: “A police search and rescue vehicle has just driven past but that’s the first service vehicle I’ve seen.”

The IT specialist had spent five hours in the same spot by 8.40pm on Thursday, but was managing to stay warm after packing a sleeping bag and some extra clothes.

“There’s no cars on the other side of the road so it must be completely blocked somewhere,” he said.

Journalism student Georgette Beacham, 28, got caught in the snow while returning from Plymouth to Falmouth.

She said: “Everyone was driving slowly but particularly on the hills, cars were jack-knifing and people were getting stuck going up hill and skidding going down hill and having to pull over.”

On one stretch of the A30 heading east towards Fraddon, a collision between a car and a lorry caused long tailbacks.

Beacham’s journey took four-and-a-half hours instead of the normal hour and 45 minutes.

Highways England said that around 100 cars became stuck on the A30 near Temple in Cornwall because of the whiteout.

A plough and a gritter have been sent to assist the stranded motorists, a spokeswoman for the organisation confirmed.

Chief Inspector Adrian Leisk, head of roads policing across Devon, Cornwall and Dorset, tweeted: “For those stuck on the A30 in Cornwall, an intensive effort is under way to clear the carriageways of vehicles to allow the gritters through. Please stay with your vehicles and we will get to you.”

The Met Office had issued an amber weather warning for snow between 2pm and 9pm on Thursday.

Its website stated the warning covers London and South East England, the South West and Wales.

A map suggested parts of Devon, Somerset, Gloucestershire, Dorset and south Wales will be among the most affected.