Hospital visitors say Nelson Mandela was smiling on his 95th birthday and South Africans celebrated upbeat reports about the former president's health after weeks of worrying that he was on the verge of death.

Children sang "Happy Birthday" on Thursday at school assemblies nationwide, and many honoured the man known as Tata or "father of the nation" by performing acts of charity for 67 minutes, symbolising Mandela's 67 years of public service.

World leaders praised the anti-apartheid leader's life of sacrifice and vision.

Andrew Mlangeni: Mandela said "let us fight for peace"

Outside the Pretoria hospital where Mandela was admitted for a recurring lung infection, well-wishers paid tribute to him and some received slices of a large birthday cake doled out from inside the compound.

Mandela remains very fragile, and many details of his medical condition have not been divulged or are tightly controlled by his family and President Jacob Zuma.

The news that his health had improved was another dramatic turn in the life of a man who became a global figure of sacrifice and reconciliation during the fight against white minority rule in South Africa.

"When I visited him today, I found him really stable, and I was able to say, 'Happy Birthday', and he was able to smile,'' Zuma said, according to the South African Press Association.

His office had recently said Mandela's condition was critical but stable, but a statement Thursday said he was steadily improving.

Zindzi Mandela: My father smiles more

Several months ago, Zuma gave an overly optimistic health assessment, but his remarks on Thursday were matched by comments from some members of Mandela's family.

Mandela is making "remarkable progress" said one of his daughters, Zindzi, after tense weeks.

Granddaughter Tukwini Mandela said the day was "bittersweet" for the family.

Thursday also marked the 15th wedding anniversary of Mandela and Graca Machel, the former first lady of Mozambique who has spent much of the time at her husband's side during his illness.

Source: Agencies