The number of lambs killed will not be known until tailing, but at an expected average farm-gate price of $80 a lamb, the cost to farmers could be measured in millions of dollars.
The Owaka Lions Club has in recent days collected up to 400 dead lambs a day from the 19km-long Owaka Valley Rd, for which farmers will receive 50c each.
Farmers say that is the tip of the iceberg, with many unable to collect all dead lambs.
Agriculture Minister David Carter will visit Southland today to see the disaster first-hand.
Federated Farmers adverse events spokesman David Rose said the visit should help Mr Carter decide about the declaration application.
Mr Rose, a farmer from Winton, said, "The biggest thing an adverse event declaration gives us is access to advice from the Rural Support Trust and recognition.
This event is one out of the box."
"The spring storm of 2010 is frankly the worst in a generation with farmers going back over 50 years for anything this bad."
He estimated half the farms in Southland - about 800 - could be affected.
On the worst affected farms, breeding ewes were also being lost.
For many farmers, it would be their worst lambing.
"You feel more like a slink truck operator than a farmer at the moment," he said.
An adverse event declaration would give affected farmers access to assistance with cleaning up, individual and family support and recovery assistance.
Clinton and Owaka are among the hardest hit areas and local farmer John Latta said the extent of stock deaths would have repercussions throughout the community, from truck drivers who would have less stock to cart, to meat workers, who would have fewer lambs to kill.
The loss will be significant for the meat industry, which already has surplus processing capacity and declining lamb numbers.
Beef and Lamb New Zealand forecast a total lamb drop this season of 28.3 million, of which 21.4 million would be killed for export, down from 2005-06 when the lamb drop was 33.8 million and lamb kill 25.4 million.
South Otago farmers spoken to yesterday were stressed and felt helpless at being unable to prevent the deaths.
Some farmers have stopped checking lambing ewes, saying that to do so disturbed those sheltering from the storm and exposed them to the elements.
A sixth day of snow, rain, wind, hail and sleet was forecast for the already battered coastal belt from Colac Bay in Southland, parts of Central Southland, the Catlins, Owaka and Clinton.
Owaka Valley farmer Ian Willocks was losing 80 to 90 lambs a day, but he was worried lambs that survived could succumb to infection in coming weeks.
Owaka farmer Nellie McNab said 25 beef breed calves had died because of the weather, even though her husband, Peter, and farm staff were working from dawn until well into the night assisting calving cows.
Keith McNab described the scene on his Owaka farm as a disaster.
Owaka Valley farmer Grant Bradfield said lambs born to ewes shorn before lambing were coping better than those in full wool, as they sought shelter to have their lambs.
"That's why we pre-lamb shear. It is one of the best tools," he said.
Mr Latta said farmers were frustrated because there was little they could do.
"We try and do our best but this is beyond our control."
Even sheltered areas were turning to bog and lambs were dying after being born in a puddle or mud.
Farmers did not like seeing animals stressed or suffering, but having six days of blizzards and wet and cold conditions was exceptional.
