Authorities have identified the strain of avian influenza as H5N2, regarded as less dangerous than the H5N1 variety, which ravaged chicken farms across Asia and crossed over to humans earlier this year, killing 24 people in Thailand and Vietnam.
The South African outbreak poses little risk to humans, but authorities were still trying to identify the source, said Dr. Johann van Wyk, head of animal health at the Department of Agriculture and Land.
The country supplies about 70 percent of the world's ostrich meat, producing about 950,000 tons a year. But the main source of ostrich revenue is from the bird's skin, which is used to make handbags, shoes, jackets and other leather goods.
The first cases were reported in Middleton, home to some of South Africa's largest ostrich farms — an industry that brings in about $200 million in export earnings annually.
Fifteen farms within a nine-mile radius of the initial outbreak have been quarantined, van Wyk said.
"We have 30,000 ostriches in that radius, and we will begin tests and culling where necessary on Tuesday," he said. "At this stage it is unlikely we will have to cull all the birds."
Police and military have also set up checkpoints up to 18 miles away to prevent the movement of birds in or out of the quarantined area.
On Friday, the government banned all poultry exports in a bid to safeguard the international credibility of its industry. South Africa imports most of its chicken meat, so the ban primarily affects ostrich farmers.
Authorities here hope to reduce the number of birds that must be culled by isolating any determined not to be carrying the virus.
Trenches have already been dug on certain farms to receive the culled birds, which will be buried and covered with quicklime to prevent further spread of the disease, van Wyk said.
By Elliott Sylvester