A massive effort is underway in South Africa to transform a soccer stadium for Nelson Mandela’s memorial and ensure tight security as world leaders and tens of thousands of people descend on the country.

Close to 100 heads of state are expected to attend the memorial for South Africa’s former president and anti-apartheid hero at the FNB Stadium in Johannesburg, which has a capacity of just under 95,000.

Mandela made his last public appearance at the same stadium for the closing ceremony of the 2010 World Cup.

Thousands of police officers will direct traffic and protect the crowds, as well as help dignitaries’ bodyguards, Lt. Gen. Solomon Makgale of the South African Police Service told The Associated Press.

As well, private security firm Sidas Security will have 1,500 guards on duty Tuesday. As late as Monday, the company was still hiring guards.

Roads surrounding the stadium will be closed off Tuesday, as will the airspace over the stadium.

With less than 20 hours to go, crews were building a stage and cutting the grass at the FNB Stadium. Bullet-proof glass was also being installed to shield world leaders.

Prime Minister Stephen Harper arrived in South Africa Monday, accompanied by former prime ministers Kim Campbell, Brian Mulroney and Jean Chretien.

NDP Leader Thomas Mulcair, the Assembly of First Nations national Chief Shawn Atleo, along with the premiers of Nova Scotia, Alberta and the Yukon also made the journey.

U.S. President Barack Obama is also scheduled to attend the memorial service, along with first lady Michelle Obama and former U.S. presidents George W. Bush, Bill Clinton and Jimmy Carter.

John Thompson, vice-president of intelligence at Strategic Capital Intelligence Group, told CTV News Channel that specific security challenges include organizing motorcades, communication frequencies and finding adequate housing for the world leaders.

Thompson, whose firm is not involved in providing security for Mandela's memorial service, said that while every international gathering is a potential target for terrorists, he would classify the threat level in Johannesburg as "low."

While there may be problems with crowds and possibly organized crime, terrorism "isn't likely," Thompson said.

Once the seating in FNB stadium is maxed out, members of the public will be redirected to three other venues that will be broadcasting the memorial service: Ellis Park Stadium, Orlando Stadium and Dobsonville Stadium.

The memorial service is expected to last about four hours, and while the program remains a closely-guarded secret, an initial program was released Monday.

Among the speakers slated to speak at the service include: South African President Jacob Zuma, Obama, Namibian President Hifkepunye Pohamba, Cuban President Raul Castro Ruz, Chinese Vice-President Li Yuanchao and UN Secretary-General Ban Ki-Moon.

Members of Mandela's family, including some of his grandchildren, will also pay tribute to the leader on Tueday.

Following the service, Mandela's body will lie in state in Pretoria's Union Buildings from Wednesday to Friday. A funeral service for Mandela will be held in Qunu, his rural hometown, on Sunday.

Thousands are also expected to attend the funeral service.

With files from The Associated Press and CTV Senior Broadcast Producer Rosa Hwang

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