"According to initial police reports, unknown gunmen stormed a Pietermaritzburg homestead and ambushed the family," police spokeswoman Lirandzu Themba said in a statement.
Police did not give a motive for the shooting. Those killed included seven women and three men, the police ministry said in a statement.
Police Minister Bheki Cele and the top management of the South African Police Service will visit the crime scene of the latest shooting later on Friday.
Mass shootings are relatively common in South Africa, which has one of the world's highest murder rates.
This report was compiled from Reuters and Agence France-Presse.