South African President Jacob Zuma is to give the keynote address next.
Ceremony organisers cut in with a musical interlude to drown out the boos from the crowd.
Pictures released today give a unique look inside Air Force One as two former and one current US President flew to Nelson Mandela's memorial
Twenty years ago the soon to be President Mandela pledged to 'wash away the stains of apartheid' - two decades on those stains remain.
Barack Obama has led the tributes to Nelson Mandela saying that South Africa's democracy is his 'cherished legacy.'