Nearly 200 rhinos were killed in South Africa in the first half of 2011, with most slaughtered in the world-famous Kruger National Park, environmental group WWF said.
South Africa lost 193 rhinos in the first six months of the year, with 126 of them killed in Kruger, one of South Africa's top tourist draws, the group said in a statement.
Last year a record 333 rhinos were killed in South Africa, which is home to about 70 percent of the world's rhino population.
"Poaching is being undertaken almost without exception by sophisticated criminals, sometimes hunting from helicopters and using automatic weapons," said Joseph Okori, WWF's African rhino programme coordinator.
"South Africa is fighting a war against organised crime that risks reversing the outstanding conservation gains it made over the past century."
South Africa's success in conservation has made the country a target for well-armed gangs. The military this year has begun patrolling Kruger in an effort to crackdown on poaching.
Authorities have arrested 123 suspected poachers so far this year, with six convictions. But the stepped-up law enforcement efforts have yet to slow the slaughter.
Poaching has soared from just 13 cases in 2007, an increase powered by demand for rhino horns in Asian traditional medicine.
"We are pleased to see more successful convictions of poachers," said Morne du Plessis, head of WWF South Africa.
"Applying strict penalties for wildlife crimes such as rhino poaching will demonstrate the South African government's commitment to maintaining this important part of the country's heritage."