Millions of South African schoolchildren sang to celebrate Nelson Mandela's 93rd birthday Monday, leading a worldwide chorus of birthday wishes sent to the anti-apartheid icon.

More than 12 million students sang a special version of "Happy Birthday" before lessons began Monday.

Mandela also received birthday wishes from South African leaders including President Jacob Zuma and from U.S. President Barack Obama.

In a statement sent Sunday, Obama called Mandela "a beacon for the global community, and for all who work for democracy, justice and reconciliation."

Mandela, who has retired from public life, is expected to spend the day with his family in his home village of Qunu, some 1,000 kilometres south of Johannesburg.

In 2009, his birthday was declared as an international day devoted to public service.

People around the world have been asked to mark the occasion by giving 67 minutes of their time to work in their local community — one minute for every year of Mandela's public service.

He became South Africa's first black president after spending 27 years in prison for his fight against apartheid.

He was awarded a Nobel Peace Prize for his efforts.

Rare public appearances

Mandela's public appearances have become increasingly rare, though he did appear at the closing ceremony of the World Cup one year ago.

Earlier this year, he was hospitalized for a few days with an acute respiratory infection. Last month, though, he held a private meeting with Michelle Obama when the first lady travelled to South Africa with her daughters.

His foundation also has recently released "Nelson Mandela By Himself," a book featuring more than 2,000 Mandela quotations on topics ranging from freedom to forgiveness to HIV/AIDS.

For many South Africans, the elder statesman is also thought of as a beloved family member and referred to by his clan name, Madiba.

'For them to be able to rise from that and forgive the people who hurt them, there's no better example than Madiba.'—Bronwen Jones, charity founder

Students at the Johannesburg School for the Blind and Partially Sighted sang and danced Monday morning as they wished their "Tata Mandela" a happy birthday.

Most of the students are fire victims from South Africa's impoverished townships and have received assistance from the Children of Fire charity.

This year, the charity held a mock trial at the school to illustrate Mandela's role in fostering reconciliation after apartheid's end. On trial: several children accused of stealing from the kitchen.

Charity founder Bronwen Jones said the lesson is especially valuable for children who have been through adversity. She said one in three of the children were burned intentionally.

"For them to be able to rise from that and forgive the people who hurt them, there's no better example than Madiba," she said.