At least 633 rhinos have been killed in South Africa this year, a record toll as demand for their horns continues to surge on the black market in Asia, the government said Wednesday.

More than 60 percent of the slaughtered pachyderms were from the vast Kruger National Park, South Africa's largest wildlife reserve and the country's top safari destination.

Rangers a week ago predicted around 20 more animals will be killed before the end of the year in the park, which boasts 40 percent of the world's rhino population.

Only the black and white rhino species are found in Africa, and environmentalists claim the black rhino is becoming critically threatened, with less than 5,000 in the wild.

The number of rhinos poached in South Africa has climbed sharply from 13 in 2007 to 333 in 2010 and 448 last year.

The total number of arrests of suspects linked to rhino poaching this year stands at 266.

Rhinos are victims of a booming demand for their horns, which some people in Asia think have medicinal properties. The medical claim is widely discredited.

South Africa and Vietnam last week signed a deal to tackle the trade.