President Jacob Zuma has described Ronnie Kasrils's spoil-your-ballot campaign as a "very funny thing", SABC radio news reported on Wednesday.

Zuma told the state broadcaster he hoped he would get an opportunity to talk to the former intelligence minister and African National Congress stalwart about the campaign he launched on Tuesday.

Zuma said the ANC, including Kasrils, had fought hard for the right to vote.

"It's a very funny thing... he [Kasrils] was not just a comrade, he was a friend.

"Maybe at some point we will have an opportunity to meet him and engage him," said Zuma.

The "Sidikiwe! Vukani! Vote Campaign" calls on South Africans to either vote for a minority party, or spoil their ballots.

"If the ANC were to lose three, four percent in this election they'll still be in power, nothing will stop that," Kasrils told reporters at the launch at Wits University in Johannesburg.

"But what that signals... is that, my God you guys [ANC] better wake up... you're not going to last for five years, you're losing more and more respect."