South

Africans have paid tribute to Nelson Mandela's legacy as the former president turned 93 today.

His countrymen and women pledged to undertake at least 67 minutes

of public service – 67 being the number of years Mandela has devoted to public service.

Mandela – affectionately known by his clan name Madiba – spent the day at his childhood home in Qunu. 

Early on Monday, about 12 million school pupils throughout the country sang"Happy Birthday"

in unison nationwide before the start of their school day..

A

group called "Bikers for Mandela" rode around the country for eight

days carrying out  volunteer service, including planting trees and painting playgrounds.

The last sighting of Mandela was at the closing ceremonies of the World Cup in South Africa

last year, where he looked frail and slightly confused.

He was hospitalised in January for an acute respiratory infection, and continues to receive medical care at home.

Under

South Africa's apartheid regime, Mandela spent 27 years in prison after

being convicted of sabotage and attempts to overthrow the government.

He was released in 1990 and became president in 1994.

The United Nations joined his foundation in urging the world to perform 67 minutes of public service.

"Tutor a child. Feed someone less fortunate. Care for

your environment. Volunteer at a hospital or community center. Be a

part of a global movement to make the world a better place," U.N. chief Ban Ki-moon sai.

U.S.

President Barack Obama, whose wife, Michelle, met Mandela last month,

said the icon is "a beacon for the global community" and for those who

fight for justice.

"Madiba sets the standard for service

worldwide, whether we are students, shopkeepers or farmers, Cabinet

ministers or presidents," the president said in a statement. "He calls

on us to serve our fellow human beings, and better our communities."

The United Nations designated July 18 as Mandela day in 2009.