Tens of thousands of South Africans converged in sorrow, celebration and pride Tuesday on Soweto's World Cup stadium, to sit side-by-side with presidents, priests and queens at a memorial service for unifying global icon Nelson Mandela.

Close to 100 world leaders were among 80,000 people expected to cram into the venue in Soweto -- the crucible of Mandela's anti-apartheid struggle -- to bid farewell to a man whose life story earned uncommon universal respect.

Despite the profound sense of national sorrow triggered by Mandela's death last Thursday, the mood was upbeat, with people determined to celebrate the memory of one of the 20th century's towering political figures.

"He's God given, he's God taken. We will never stop to cherish him," said Shahim Ismail, who took a day off from the sports academy he runs in Johannesburg to attend the event.

With access offered on a first-comer basis, crowds began gathering before daybreak and, as the gates opened, they swarmed into the stadium, looking for the best vantage point on the sloped terracing.

Wrapped in the South African flag or yellow-green coloured shawls printed with the slogan "Mandela Forever," they danced and sang -- oblivious to a persistent morning drizzle.

"This is once in your life. This is history," said Noma Kova, 36. "I didn't want to watch this on TV."

Many of the songs flowing from the terraces harked back to the apartheid-era struggle, but the atmosphere was one of inclusion.

News of Mandela's death at his home in Johannesburg resonated around the world, triggering a wave of loving admiration from political and religious leaders, some of whom agree on little else.

Global rivalries put on pause

The presidents of the United States and Cuba were among those sharing the memorial stage, pausing rivalries that date back to the Cold War to pay tribute as millions around the world looked on.

The Indian and Brazilian presidents will also deliver eulogies, reflecting the extraordinary global reach, popularity and influence of one of the 20th century's best-loved statesmen.

Obama and his wife Michelle flew in on Air Force One early in the morning, together with former president George W. Bush and his wife Laura.

Two other ex-presidents, Bill Clinton and Jimmy Carter, were arriving separately.

The memorial event was part of an extended state funeral that will culminate in Mandela's burial on Sunday in the rural village of Qunu where he spent his early childhood.

Security was tight around the Soweto stadium, with military helicopters flying overhead and marshals helping police to keep the crowds moving.

Four of Mandela's grandchildren were set to speak for his family.

Although Mandela had been critically ill for months, the announcement of his death was a body blow for this recently reborn nation.

He had been out of public life for more than a decade, but South Africans looked to his unassailable moral authority as a comforting constant in a time of uncertain social and economic change.

'He really was like a magician'

On the eve of the memorial, Nobel laureate Desmond Tutu described Mandela as a "magician" who conjured a united nation out of a country teetering on the brink of civil war.

"Everybody was saying we would go up in flames," he said.

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

A single candle was lit Monday in Mandela's tiny prison cell on Robben Island, where he spent the harshest of his 27 years in apartheid jails, before emerging to lead his divided country into a multi-racial democracy.

On Monday, his eldest daughter Makaziwe Mandela told how her father spent a "wonderful" week surrounded by family before he died.

"The children were there, the grandchildren were there ... so we are always around him, even at the last moment," she told the BBC.

Ahead of the burial in Qunu, Mandela's body will lie in state for three days from Wednesday in the amphitheatre of the Union Buildings in Pretoria where he was sworn in as president in 1994.

Each morning, his coffin will be borne through the streets of the capital in a funeral cortege, to give as many people as possible the chance to pay their final respects.

British Prime Minister David Cameron, French President Francois Hollande and Afghan President Hamid Karzai were all on the state funeral guest list.

Africa was represented by Nigeria's Goodluck Jonathan and more than a dozen other heads of state and government.

Talk show queen Oprah Winfrey and singer-activist Bono, as well as British billionaire Richard Branson and musician Peter Gabriel were expected to be among the celebrity mourners.

In the Soweto stadium, a radiant Musa Mbele, his clothes drenched by the rain declined the offer of an umbrella.

"If he was able to stay behind bars for 27 years for us, what is one day, just one rain-drenched day?" he said.