Hill farmers in Wales face one of their worst crises in 60 years as the melting snow reveals the carcasses of thousands of heavily pregnant ewes and new-born lambs.

Many animals remain buried under snow drifts, farmers have been unable to get food to starving survivors and the bitter weather forecast to continue for at least a fortnight.

"It's the worst we've known at this time of year since 1966 when I left school," said Emyr Jones, president of the Farmers Union of Wales, who keeps 1,000 ewes on land near Lake Bala on the edge of Snowdonia in north Wales.

"We won't know exactly how bad the situation is until the snow goes finally, but we know losses will be high. The lambs are being frozen to death before they can even stand. It's impossible for farmers to find some sheep in the mountainous areas," he said.

Farmers who were digging sheep out of 20ft snowdrifts across north and mid Wales throughout the holiday weekend predicted higher prices for Welsh lamb and said many hill farmers could be forced to give up because of the extra costs.

Gareth Wyn Jones and his family, who farm 2,000 acres in the Carnedd range, have so far dug out 70 ewes but fear they have lost many hundreds. "Some sheep are trapped in catacombs under the snow, so can be pulled out. We found two ewes that had lambed, but their lambs had frozen to death. We found another eight heavily pregnant ewes and managed to save them and they were able to lamb."

He and other hill farmers called for the Welsh government to suspend EU rules to allow them to bury dead animals where they fall, instead of having to pay up to £20 to have each dead animal collected and disposed of by knackers' yards.

Welsh food and natural resources minister Alun Davies said: "I [have ] asked my chief veterinary officer, Christianne Glossop, to look urgently at what the Welsh government can do to alleviate the burden on farmers. I will respond early next week."

Ten days after one of the worst snowstorms in 50 years to hit north and mid Wales, farmers reported that they were taken by surprise by its intensity which saw three feet of snow fall in some places in under 24 hours.

Glyn Roberts, who keeps sheep on the Arunweg mountains south of Bettws y Coed in Snowdonia, said he was one of the lucky few who managed to get most of his sheep into the farmyard before the storm hit. His sheep mostly survived because he managed to build a temporary shelter for them. "We have been flat out. Every shed is packed out and we cannot get any back on the mountain. I have lost some but there must still be thousands still there. Its impossible to find them.

"There are still 20ft high drifts. Lambs are being frozen to death before they can even walk. Ewes are walking away from their lambs. The snow is just beginning to melt and we are starting to see the full extent of the disaster. But the drifts are so bad we don't know what's under them. Its a case of hoping for the best."

Many farmers are now desperate for animal feed but costs are spiralling, said Helen Davies, manager of the Welsh region of the national sheep association.

"The hill farmers have had it bad. It's going to have serious knock-on effects. The cold weather came right at the height of the lambing season. The shock of the cold made some of the ewes lamb earlier. The animals caught in the storm sheltered below walls but were quickly buried by snow," she said.

As the drifts begin to melt in the lower areas and farmers get access to their fields, they are being met by the horrific sight of animals who survived the snow and ice but have had their eyes pecked out by crows and been half eaten by foxes, she said. "It's not unheard of to have snow drifts at this time of year but usually it lasts for only two days or so. It's now 10 days, roads are still shut and it is still freezing," said Nick Fenwick, policy director of the Farmers' union of Wales.

"It comes on the back of the collapse of lamb prices last year, torrential rains that have reduced harvests, very little grass on the sodden hillsides. Hill farmers are always on the edge. Something like this could push people over," he said.

"There must be a fall in the lamb crop and an increase in prices. Whether the higher prices will be enough to cover the costs of providing extra feed we don't know," he said.

"Wales is now the only country in the EU that no longer gives extra payments for 'less favoured' areas. The ending of the upland grant last year means that for the first time in 60 years the cheque that people used to rely on to pay winter fodder bills is not there."

"It's been catastrophic. It's survival of the fittest now," said David Pittendreigh, chair of the Sheep Association of Wales.