JOHANNESBURG -- Doctors are doing all they can to for Nelson Mandela as the 94-year-old icon spent a fourth day in the hospital for a recurring lung infection, South Africa's president said Tuesday, as two of Mandela's daughters visited their father.
In a possible sign of the seriousness of Mandela's condition, daughter Zenani Mandela -- South Africa's ambassador to Argentina -- arrived at the hospital to see her father. Former wife Winnie Madikizela-Mandela also visited.
In an interview, Zuma called Mandela's situation "very serious" but said he has stabilized.
"We need him to be with us and I'm sure that all the messages that have been pouring in to wish him (a) quick and speedy recovery, they're highly welcome," Zuma told broadcaster SABC, adding later: "And we certainly join everyone to say he should recover quickly, and I'm sure, knowing him as I do, he's a good fighter, he will be with us very soon."
White House spokesman Jay Carney said that President Barack Obama, the first lady and everyone at the White House wished Mandela a "speedy recovery."
In a Johannesburg suburb, school children gathered outside his home on Tuesday and sang songs expressing hope the former president would recover.
Mandela, the leader of South Africa's anti-apartheid movement, spent 27 years in prison during white racist rule. He was freed in 1990, and then embarked on peacemaking efforts during the tense transition that saw the demise of the apartheid system and his own election as South Africa's first black president in 1994.
His hospitalization in Pretoria is Mandela's fourth time being admitted to a hospital for treatment since December. His last discharge came April 6 after doctors diagnosed him with pneumonia and drained fluid from his lung area.
At Johannesburg's Apartheid Museum on Tuesday, visitors walked through an exhibit showcasing the life of Mandela amid a feeling in the country this hospitalization may be more serious than others.
"All these admissions to the hospital has been preparing us for this, that this may be the end, and that is enough to tell us this is very serious," said Father Victor Phalana of Cathedral of the Sacred Heart in Pretoria, who was touring the museum with two Catholic priests from Uganda.
Outside Mandela's Johannesburg home, school children from the Rainbow Hill Christian School sang words of encouragement. "We love you Mandela ... get well, get well," they sang.
Lebogang Serite, a 12-year-old student at the school, said she "couldn't be in a white people's school" had it not been for Mandela's anti-apartheid efforts. "He means a lot to me because he fought for the country. I couldn't be in a white people's school," she said.
"I know that if he was able to speak, he was going to play with them today. Unfortunately, wherever he is, he's not well, but I know that he worked very, very hard for us. That's why we are here," said Mama Zodwa, a 57-year-old teacher from the school.
On Monday a foundation led by retired archbishop Desmond Tutu described Mandela as an "extraordinary gift" and offered prayers for his comfort and dignity. The Desmond and Leah Tutu Legacy Foundation described Mandela as "the beloved father of our nation."
Mandela is seen by many around the world as a symbol of reconciliation because of his peacemaking role when white racist rule ended in South Africa. Tutu, 81, was also vigorous campaigner against apartheid, which ended when all-race elections were held in 1994 and Mandela president.
Like Mandela, Tutu was awarded the Nobel Peace Prize for his efforts on behalf of his compatriots. Mandela shared his prize in 1993 with F.W. de Klerk, the last president of the apartheid era.
In its brief statement on Mandela's health, the presidency said Zuma "reiterates his call for South Africa to pray for Madiba and the family during this time," referring to Mandela by his clan name.
Mandela has been particularly vulnerable to respiratory problems since contracting tuberculosis during 27 years as the prisoner of the white racist government. The bulk of that period was spent on Robben Island, off the coast of Cape Town where Mandela and other prisoners spent part of the time toiling in a stone quarry.
He was freed in 1990, and then embarked on peacemaking efforts during the tense transition that saw the demise of the apartheid system and his own election as president in 1994.
The former leader retired from public life years ago and had received medical care at his Johannesburg home until his latest transfer to a hospital.