Retired Anglican Archbishop Desmond Tutu, center, arrives at the Nelson Mandela Centre of Memory in Johannesburg, South Africa, Monday, Dec. 9, 2013. Scores of heads of state and government and other foreign dignitaries, including royalty, are beginning to converge on South Africa as the final preparations for Tuesday's national memorial service for liberation struggle icon Nelson Mandela are put in place.(AP Photo/Muhammed Muheisen)

JOHANNESBURG - South Africa prepared Monday for a massive memorial in a soccer stadium honouring Nelson Mandela, where an eclectic mix of world leaders will eulogize the anti-apartheid icon before a crowd of nearly 100,000 mourners.

As a prelude to the stadium event, United Nations Secretary General Ban Ki-moon and retired Archbishop Desmond Tutu spoke at an event at the Nelson Mandela Centre of Memory Monday night.

"What a fantastic gift God gave to us in this Mandela, who quickly became an icon, a global icon of forgiveness, of generosity of spirit," Tutu said.

"He really was like a magician with a magic wand, turning us into this glorious, multi-colored, rainbow people," said Tutu.

At the Soweto stadium where Mandela made his last public appearance at the 2010 World Cup, workers busily constructed a stage protected by bulletproof glass for Tuesday's memorial.

Police promised "thousands" of officers would secure the stadium, though security appeared lax Monday and a security company owner used his small car as a mobile office to hire guards just at the stadium.

Nearly 100 heads of state are expected at the 95,000-capacity FNB Stadium, where some mourners are already camped out to be the first ones inside. Authorities expect overflow crowds to watch the event at nearby stadiums as well, saying they'd shut off access if the crowds grow too large.

Officers will direct traffic, protect mourners and help the bodyguards of visiting dignitaries, Lt. Gen. Solomon Makgale, a spokesman for the South African Police Service, said Monday.

"We will be on hand to make sure people are able to grieve in a safe environment," Makgale told The Associated Press.

Makgale said a joint taskforce of police, diplomats and intelligence service personnel already have been making plans and talking to the foreign delegations who plan to attend the ceremony.

Makgale said police were prepared for Tuesday's event, which also will include speeches from Mandela's family and friends.

"Whether we have 10 heads of state coming or 70 or 100, we do have the capacity and plans in place to facilitate their movement," Makgale said.

United States President Barack Obama and his wife Michelle left Washington for Johannesburg aboard Air Force One on Monday. In a rare get-together, they were joined by former President George W. Bush, his wife Laura and former first lady Hillary Clinton. Former Presidents Bill Clinton and Jimmy Carter are travelling separately to South Africa.

A program released by the South African government showed Obama would speak, as would United Nations Secretary-General Ban Ki-moon and Chinese Vice-President Li Yuanchao. Others speakers include Brazilian President Dilma Rousseff, Namibian President Hifikepunye Pohamba, Indian President Pranab Mukherjee and Cuban President Raul Castro. South African President Jacob Zuma will give the keynote address.

Though security remains a concern, an AP reporter walked unsearched into the stadium Monday by showing only a national press card issued in Europe. It took about three minutes before a security officer asked journalists to leave the stadium's field. However, reporters freely roamed throughout the stadium and walked the aisles to see the ongoing stage construction.

Officials from the U.S. Consulate in Johannesburg also toured the venue Monday, but declined to speak to journalists.

Meanwhile, a private security firm called Sidas Security was still hiring guards for Tuesday's event on Monday, using a compact car as an office. Sidas manager George Mathabe said the company will have 1,500 guards on duty Tuesday.

"I'm doing this from the bottom of my heart, just to thank Tata," Mathabe said, using the Xhosa word for father as an endearment name for Mandela. "My son is coming tomorrow as a visitor too. He's going to live in a free country. He's going to be able to do whatever he likes thanks to Tata."

Roads several square kilometres (miles) around the stadium will be closed Tuesday, and people will have to walk or take public transport to the stadium.

Mandela died Thursday at age 95. After the stadium memorial on Tuesday, Mandela's body will lie in state at the Union Buildings, the seat of government in South Africa's capital, Pretoria, from Wednesday to Friday. He will be buried Sunday in Qunu, the Nobel Peace Prize laureate's rural hometown in Eastern Cape Province.

South Africa's parliament held a special session Monday in honour of Mandela. Kgalema Motlanthe, the country's deputy president and a member of Mandela's African National Congress political party, opened the proceedings with a speech describing how the icon's death caused a "sweeping feeling of sorrow" around the world.

"He belongs to all humanity," Motlanthe said. He added: "Mandela's ideals saturate the face of the Earth."

Helen Zille, the leader of the opposition Democratic Alliance political party, said South Africa inherited "an enormous responsibility" from Mandela to ensure everyone had "freedom you can use."

"He has handed the baton to us and we dare not drop it," Zille said.

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Follow Jon Gambrell on Twitter at www.twitter.com/jongambrellAP.

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Follow Juergen Baetz on Twitter at www.twitter.com/jbaetz.

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Associated Press writers Christopher Torchia in Cape Town, South Africa, Julie Pace in Washington and Ray Faure in Johannesburg contributed to this report.

News from © The Associated Press, 2013