South Africa nearly doubled its presidential spousal budget after polygamous leader Jacob Zuma took office with three wives and 20 children, a minister said on Tuesday.

The budget jumped to R15.5-million last year, up from eight million rand under former president Thabo Mbeki, said the minister in the presidency, Collins Chabane.

Zuma faced national outrage in January over an out-of-wedlock daughter born in October to the daughter of a top World Cup organiser, with questions asked about his fitness for office.

She is the 20th child for Zuma who has been married five times.

The president's children are defined as financially dependent until 27 years in age, if studying full-time and unmarried.

"The policy applies to children of the president regardless of the marital status of the child's parents," Chabane said in a written response to an opposition question.

Zuma's wives receive a personal secretary and researcher, domestic and international travel, cellular phones, equipment like laptops and printers, and a daily allowance during official trips.

While having no specific roles or responsibilities, the wives are expected to support the president at state and official functions.

Zuma's three wives support causes such as health, agriculture and food security, and orphans and vulnerable children.