Leaders, celebrities and admirers are marking the 91st birthday of former South African President Nelson Mandela.

Mr. Mandela celebrated Saturday at his home in Johannesburg with family and several prominent African leaders, including South African President Jacob Zuma.

Mr. Zuma, who also heads Mr. Mandela's African National Conference party (ANC), helped lead those in attendance in the singing of "Happy Birthday."  He told the former leader not to worry because the ANC is in "good hands."

Nelson Mandela's charities have declared this the first annual Mandela Day, and are encouraging people around the world to continue the Nobel Peace laureate's legacy by working on projects in their communities. 

In New York, Mr. Mandela will be celebrated by a star-studded concert at Radio City Music Hall, featuring performances by Stevie Wonder, Aretha Franklin, Wyclef Jean and Alicia Keys. 

French first lady Carla Bruni-Sarkozy also is scheduled to sing at the gala in her first public performance since marrying President Nicolas Sarkozy.

In Soweto, American tourists visiting a museum in a home where Mandela once lived were inspired by the celebrations and made a spontaneous $300 donation to a nearby park for children in wheelchairs.

On Wednesday, a Mandela Day dinner was hosted in New York by former U.S. President Bill Clinton and Mr. Mandela's wife, Graca Machel.  Mr. Clinton said the world owes Mr. Mandela a debt for "leaving public office with grace, but continuing with his responsibilities."

Mr. Mandela spent 27 years in prison for his fight against South Africa's apartheid.  Released from prison in 1990, he was elected South Africa's first black president in 1994.  He has since received numerous awards for his life's work.