|Mandela became president after spending 27 years in prison for fighting the apartheid regime [EPA]
South Africans are celebrating Nelson Mandela's 93rd birthday with millions of schoolchildren singing for the anti-apartheid icon, while others in the country rallied to do charity work in honour of his contributions as a rights activist.
More than 12 million schoolchildren sang a special version of "Happy Birthday" before lessons began on Monday, in an event coordinated by his official Nelson Mandela Foundation, the government and other groups.
In a statement, the foundation said that by organising the campaign it "hopes to mobilise the entire society to promote education, unity and social cohesion in honour of Madiba".
For many South Africans, the elder statesman is also thought of as a beloved family member and referred to by his clan name, Madiba.
Mandela became South Africa's first black president in 1994 after spending 27 years in prison for his fight against apartheid. He was awarded a Nobel Peace Prize for his efforts.
On Monday, the former statesman also received birthday wishes from world leaders including South African President Jacob Zuma, who praised Mandela's contribution to South Africa.
In a statement, Zuma said everyone knew South Africa would be different country the moment Mandela stepped out of prison.
"He showed us that despite the divisive racial oppression and hardships that this nation had gone through, it is not only possible, but necessary to embrace one another and to reconcile the South African people," Zuma said.
Zuma, who planned to visit Mandela in Qunu after meeting with visiting British Prime Minister David Cameron in Pretoria, used the occasion to call for greater efforts to end poverty.
"We have achieved a lot, but we must still work further to eradicate poverty and improve especially the lives of children, because Madiba loves them so much.".
A mesage from US President Barack Obama, called Mandela "a beacon for the global community, and for all who work for democracy, justice and reconciliation".
In 2009, Mandela's birthday - 18 July - was declared as an international day devoted to public service.
It is observed as Mandela Day, recognised by the United Nations as a global call to volunteer for good causes for 67 minutes - one minute for every year Mandela spent in active politics.
South Africans cleaned and painted schools, orphanages and clinics, while others donated food, clothes, books and toys to charity.
UN Secretary General Ban Ki-moon urged the world to observe Mandela's call to carry out volunteer work.
"Everybody remembers and, indeed, needs an inspirational figure who has played a signal role in their lives. Nelson Mandela has been that role model for countless people around the world," Ban said.
Mandela, who has retired from public life, is expected to spend the day with his family in his home village of Qunu, some 1,000km south of Johannesburg.
"He's just going to have a relaxing time with his family," Nelson Mandela Foundation spokesman Sello Hatang said.
Increasingly frail with age, Mandela was last seen in public just before his 92nd birthday, when he and his third wife Graca Machel made an appearance at the FIFA World Cup final in Johannesburg.
On Sunday, he spent the day with his family in Qunu. He looked well in photographs taken with his family and published on his foundation's website.
Mandela is revered for having ushered in democracy and for his personal sacrifices in fighting the apartheid regime. He used his warmth, dignity and self-deprecating humour to help heal racial divisions and opened a process of reconciliation.