South African authorities are struggling to cope with arrangements for the public memorial of former president Nelson Mandela as world leaders and royals have started pouring in on an unprecedented scale.

"The world literally is coming to South Africa. I don't think it has ever happened before," said South Africa's chief of public diplomacy Clayson Monyle, referring to the number of world leaders who will be attending the ceremony at the FNB football stadium in Johannesburg.

During the final hours on the eve of the ceremony, workers constructed a makeshift stage, well protected by bulletproof glass for the dignitaries.

The authorities have said "thousands" of police personnel have been deployed inside and outside the stadium as part of security measures.

"Having so many heads of state is not a security headache for us. We've learned over the years," said police spokesperson Solomon Makgale.

Officials expect the 95,000-capacity football stadium will not be enough to accommodate the crowds and have set up large screens in nearby stadiums to take care of the overflowing people. More than 120,000 people will be able to watch the ceremony at the three overflow stadiums in Johannesburg.

Scores of people camped outside the main stadium overnight to gain access to the ceremony. Shortly after the gates were opened, people started rushing in as the numbers keep swelling.

Hundreds of people are singing and dancing inside the stadium in praise of South Africa's first black president, popularly known by his clan name Madiba.

Pointing at the earlier successful events of rugby and football world cups and the UN Climate Change summit, South African minister Collins Chabane, who is overseeing the Mandela's mourning events, said: "For those who predict chaos, we are used to it. It's not new and all the time, they have been proved wrong."

He added: "I said to the Secretary General of the United Nations, if you wanted to call a General Assembly, you could do it here rather than find another venue, they're all here."

Citing security concerns, South African authorities, however, have advised heads of state not to attend the funeral in Qunu, where Mandela will be buried on Sunday (15 December).

"Nobody will be prevented from attending..., however, given the size and the scale of the operation and the size of the delegation and the limited infrastructure in the area, we advise [not to attend]," Chabane told reporters.