Hospital visitors say Nelson Mandela smiled and nodded Thursday — 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 at school assemblies nationwide, and many honoured the man known as "the father of the nation" by performing acts of charity for 67 minutes, symbolizing Mandela's 67 years of public service. World leaders praised the anti-apartheid leader's life of sacrifice and vision.

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.

"We don't only recognize him on this day. We put smiles on other people's faces, we donate to other people less fortunate," said Thato Williams, a 13-year-old student at Melpark Primary School in Johannesburg, where 700 students gathered in a hall filled with posters created to honour Mandela's contributions to peace and education.

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

The anti-apartheid leader was taken to a Pretoria hospital on June 8 for treatment for a recurring lung infection. In previous announcements, the government said he was in critical but stable condition. Court documents filed by Mandela's family earlier this month had said Mandela was on life support.

Mandela is making "remarkable progress," said one of his daughters, Zindzi, on Thursday, after tense weeks in which some South Africans talked about the possibility that Mandela was on the verge of dying.

"We look forward to having him back at home soon," the South African Press Association quoted Zindzi Mandela as saying during the government rollout of a digital ID card system. 

Ndileka Mandela, a granddaughter of Mandela, poured soup for poor children at a charity event and said her family had been unsure about whether her grandfather would live to see his birthday.

"But because of the fighter that he is, he was able to fight a repressive system, and he was able, through God and everybody's prayers, to make it today," she said.

U.S. President Barack Obama issued a statement extending 'warmest wishes' to the Mandela family:

"We will forever draw strength and inspiration from his extraordinary example of moral courage, kindness, and humility...   May Nelson Mandela’s life of service to others and his unwavering commitment to equality, reconciliation, and human dignity continue to be a beacon for each future generation seeking a more just and prosperous world."

'It still gives me chills'

At the British Open in Scotland, Tiger Woods recalled his 1998 meeting with Mandela as an experience he would "never, ever forget." 

"It still gives me chills to this day, thinking about it," Woods said this week.

'The energy that he has, that he exudes it unlike any person I've ever met.'—Golfer Tiger Woods

"A gentleman asked us to go into this side room ... and we walked in the room and my dad and I were just kind of looking around. And I said, `Dad, do you feel that?' And he says, `Yeah, it feels different in this room,' [and] probably 30 seconds later, I heard some movement behind me and it was President Mandela folding up the paper. And it was pretty amazing. The energy that he has, that he exudes, is unlike any person I've ever met."

Many South Africans volunteered 67 minutes for charity to match what organizers said were the 67 years of public service by Mandela, leader of the fight against white minority rule.

President Zuma opened low-cost housing for poor black and white families in the Pretoria area. South Africa is struggling with high unemployment, labor unrest, service delivery shortcomings and other social challenges that have dampened the expectations of a better life for black South Africans after the end of apartheid two decades ago.

si-mandela-balloons-04741954

South Africa celebrated Nelson Mandela's 95th birthday with acts of charity. (Ben Curtis/Associated Press)

Retired archbishop Desmond Tutu helped to paint a school outside Cape Town, saying Mandela makes South Africans "walk tall" and urging compatriots to refrain from divisive behavior.

Elsewhere, social workers, military commanders and private company employees others planted trees, cleaned classrooms and donated food, blankets and other basic necessities in poor areas. Doctors administered eye tests, inoculations and other medical treatments.

International Day

The U.N has declared July 18 as Nelson Mandela International Day as a way of recognizing the Nobel Peace Prize winner's contribution to reconciliation. 

Mandela was jailed for 27 years under apartheid and led a difficult transition from apartheid to democracy, becoming president in all-race elections in 1994. He served one five-year term, evolving into a global statesman and pursuing charitable causes after that. He retired from public life years ago.

"South Africa is a better place today than it was in 1994 and this is because of the contribution made by Madiba and his collective," the ruling African National Congress, once led by Mandela, said in a statement.

si-mandela-card-04741952

A birthday card made by school children. Winnie Madikizela-Mandela, Mandela's former wife, said the country can 'carry on' should he die. (Denis Farrell/Associated Press)

The ANC was the leading liberation movement during apartheid, and has dominated politics since the end of white rule. However, it has come under increasing criticism because of corruption scandals and frustration over poverty and other problems.    

In recent months, the ANC and opposition groups have sought to emphasize their connections to Mandela's legacy in the fight for democracy, leading to accusations of political opportunism on both sides.

'Respectful contemplation'

F.W. de Klerk, the last president of the apartheid era, said in a statement that Mandela's birthday "should be a time for quiet and respectful contemplation — and not for unseemly squabbling over the ownership of Mr. Mandela's heritage."

De Klerk shared the Nobel prize with Mandela in 1993 because he effectively negotiated his own government out of power, working on a political transition with Mandela that allayed fears of all-out racial conflict.

Mandela's former wife said she wanted to reassure South Africans who fear the eventual death of Mandela, a unifying figure, would open the way to unrest. 

"There are sometimes prophets of doom who say the country will come to a standstill," said Winnie Madikizela-Mandela, herself a prominent figure in the anti-apartheid movement, in an interview with South Africa's Radio 702.

However, she said: "The country will solidify, come together and carry on."