A farmer has described the devastating impact of the bluetongue outbreak after losing almost 25 sheep and lambs.
The virus, which affects sheep and cattle and is spread by biting midges, has prompted warnings from some farmers that it could become the sector's biggest crisis since the foot-and-mouth disease outbreak.
Prime Minister Andy Burnham visited a farm in Truro, Cornwall, on Saturday and said the virus was "very much at the top of our agenda" and that work was being done "to get the vaccine to the farms" where it was needed.
Kim Dart, who farms near South Molton in Devon, said she dreaded checking her flock each day because more animals were dying despite efforts to protect them.
Figures from the Department for Environment, Food and Rural Affairs (Defra), external on Sunday showed there were 258 affected sites in Devon and 96 in Cornwall, with the south-west of England being the most impacted area of the UK.
Speaking as she examined sick lambs, Dart explained that many were suffering with severe nasal discharge and painful sores in their mouths.
"We didn't see it coming on this scale," she said.
"We'd heard about it but we didn't expect it to be quite as overwhelming really.
"One minute you think that they're doing OK and then suddenly they die."
The sickest sheep had been brought indoors so they can receive extra food, water and care, she added.
Another farmer, Ian May, from Devon, said: "This year it is much worse than we thought it was going to be.
"I think we were lulled into a false sense of security last year."
May suggested weather conditions may have contributed to the rapid spread of the virus but he said the exact reason remained unclear.
Vet Ben Odbert said vaccination was vital to protect livestock.
"Bluetongue has been a nightmare, I'm afraid to say," he said. "It's really hit hard."
Burnham said work was being done to "bring the vaccine forward".
He said: "I know the issue is now of access to that vaccine."
He said the government was talking to the National Farmers' Union about concerns around access and was working hard "to get the vaccines where it is needed".
Vaccinating livestock has also created a significant financial burden for farmers.
Devon Farmer Tells of Sudden Deaths From Bluetongue