Mourners placed floral tributes on a fence outside the building, also known as the "People's Cathedral", beside a black and white portrait of the man they affectionately called 'the Arch'.
Wayne Andrews came to pay tribute, saying "He was a very, very humble man, a man of integrity and a very sincere, honest man."
"Speaking truth to power and calling out the ill elements of our new democracy and ensuring that we have a sense of hope for new leadership," said mourner Marlene Bhana.
Tutu won the Nobel Peace Prize in 1984 in recognition of his non-violent opposition to white minority rule. A decade later, he witnessed the end of that regime and chaired a Truth and Reconciliation Commission to unearth the atrocities committed under it.