Over 150 public viewing sites will be open across the nation for people
Before the gates opened, large crowds of mourners had queued for hours to bid farewell to one of the world's most loved statesmen, reports Xinhua.
"I was here before 2 a.m. I did not want to miss this day. I am here to say thank you, rest in peace Madiba," said 31-year-old Amukelani Mazibuko who came from Thembia, about 80 km from the venue.
Mandela, South Africa's first black president, died at his Johannesburg house Dec 5 at the age of 95.
"This is history in the making," Mbuyiselo Nyanda of Soweto said.
More than 100 heads of state and government, as well as current and past presidents, will attend the memorial service. International and regional organisations will also be represented. Key dignitaries include UN Secretary General Ban Ki-moon and African Union Commission Chairwoman Nkosazana Dlamini Zuma.
"I want to be party of this crowd saying goodbye to Madiba. Go well, African hero," said another mourner Mohapi Nkoeneane.
Nomvula Mokonyane, Gauteng province premier, said Tuesday that the provincial government beefed up free public transport with 740 extra trains to make it 5,000 in total to carry mourners to the stadium.
The national government said over 150 public viewing sites will be open across the nation for people who cannot make it to the stadium.
Outside the stadium, mourners sang songs in praise of Mandela, some bursting into tears.
"Nelson Mandela, Nelson Mandela Haunaye ofana niwena (Nelson Mandela, Nelson Mandela there is none like you)," they sang.
"Tata (father) was a true comrade," Amukelani Bhekisile Gaza said.
"He was a true revolutionary," 29-year-old Ncamisile Khumoyame said, as a group of young men lay on the wet ground, imitating anti-apartheid struggle veterans.
Mandela's body will be taken from the FNB stadium to the Union Buildings in Pretoria where it will lie in state for three days, beginning Dec 11.
From there it will be taken to Qunu in the Eastern Cape province, Mandela's native place where he would be buried Dec 15.