The memorial service is due to start at 11:00 local time and is expected to last four hours.
It is also be shown on big screens at three "overflow" stadiums.
South African President Jacob Zuma will make the keynote address, and other tributes will come from Brazilian President Dilma Rousseff, Chinese Vice-President Li Yuanchao, President Hifikepunye Pohamba of Namibia and Indian President Pranab Mukherjee.
U.S President Barack Obama, Cuban President Raul Castro and UN Secretary General Ban Ki-moon will also address the service, as will four of Mr Mandela's grandchildren and Andrew Mlangeni, Mr Mandela's friend and fellow former Robben Island prisoner.
Today's service is part of a series of commemorations leading up to the funeral on Sunday.
Share your memories of Mandela and light a candle for him on his profile at www.remembered.co.za.
Image: © Getty
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