A South African activist who spoke out against attacks on white farmers has been found stabbed and beaten to death on her own farm.

Annette Kennealy, 51, was killed on a smallholding in Limpopo province on either Monday night or Tuesday morning where she had been staying with an employee, police said.

The alarm was raised by Ms Kennealy's mother, Kim Labuschagne, after she tried and failed to get in touch with her daughter on Tuesday.

A male relative then went to the farm where Ms Kennealy's body was found face-down in a pool of blood. 

Police spokesman Colonel Moatshe Ngoepe said Ms Kennealy was found with 'multiple stab wounds'.

Marius Mueller, director of Afrikaner campaign group AfriForum, told Marelo Media that Ms Kennealy had been found with head wounds.

She was found laying on her stomach, had wounds to her left eye and an open wound on her forehead, he said.