100 years since his birth, S Africa pays tribute to Mandela

South Africa today marked 100 years since Nelson Mandela's birth with a "town hall" forum hosted by Barack Obama and a walk led by the anti-apartheid leader's widow among a series of tributes.

His birthday on July 18 is marked annually around the world as "Mandela Day", and the Nelson Mandela Foundation called for people to "take action and inspire change" in his name on the centenary year.

Obama, speaking to 15,000 people at a stadium in Johannesburg yesterday, gave an emotional address recalling the "wave of hope that washed through hearts all around the world" when Mandela was released from jail in 1990.

"Through his sacrifice and unwavering leadership and, perhaps most of all, through his moral example, Mandela... came to embody the universal aspirations of dispossessed people," Obama said. "(He) shows those of us who believe in freedom and democracy we are going to have to fight harder."