Nelson Mandela was responding positively to treatment Thursday after being readmitted to hospital with a lung infection, the latest health scare for the much-loved anti-apartheid icon.
President Jacob Zuma sought to reassure South Africans that Mandela was in good hands and there was no need to panic.
"The country must not panic, Madiba is fine," Zuma told the BBC, referring to South Africa's first black president by his tribal name.
The 94-year-old, who has had several recent health scares, was hospitalised just before midnight on Wednesday and is expected to spend a second night in care.
"The doctors advise that former president Nelson Mandela is responding positively to the treatment he is undergoing for a recurring lung infection," Zuma's office said in a short statement.
The Nobel peace laureate was conscious when he was admitted, presidency spokesman Mac Maharaj told AFP.
But it is the second time this month that Mandela has spent the night in hospital, after a stint to undergo checkups, which followed a nearly three-week stay in December.
Then Mandela was treated for another lung infection and for gallstone surgery, after which he was released for home-based care.
The series of hospitalisations has seen an outpouring of prayers, but has also seen South Africans become increasingly fatalistic about the future of their national hero.
"In Zulu, when someone passes away who is very old, people say he or she has gone home. I think those are some of the things we should be thinking about," Zuma said.
He earlier wished Mandela a quick recovery and asked for people around the world to pray for him.
"We appeal to the people of South Africa and the world to pray for our beloved Madiba and his family and to keep them in their thoughts," he said.
Mandela is adored in South Africa where he is seen as the architect of the country's peaceful shift to democracy after apartheid.
Nearly twenty years after he came to power he remains a unifying symbol in a country still gripped by racial tensions and deep inequality.
A series of labour unrest, violent crimes, grinding poverty and corruption scandals have effectively ended the honeymoon enjoyed after Mandela ushered in the "Rainbow Nation."
"He is the voice that holds the country together," said Kasturi Pandaram in Durban, reacting to news of his hospitalisation.
"He's been a stalwart and I think if anything should happen to him now, with the state the country is in, I think it's going to fall apart," she said.
While Mandela the symbol bestrides South African politics, the man has long since exited the political stage.
He has not appeared in public since South Africa's football World Cup final in 2010, six years after retiring.
-- Hometown villagers 'wish him long life' --
The name and location of the hospital were not disclosed, to allow the medical team to focus on their work and to shield the family from the intense media interest.
"We know they are going through a difficult time and we want to ensure that their privacy is maintained," Maharaj said.
Revered at home and abroad, the ailing Mandela has grown increasingly frail away from the public eye.
Mandela's December hospital stay was his longest since he walked free from 27 years of apartheid jail in 1990.
News of his latest ill health was slow to reach Qunu, his rural childhood Eastern Cape village where he had spent recent years before leaving in December.
"Most of the people in the village don't know even that he is in hospital," Zimsile Gamakulu, a local guide and also of the Madiba clan, told AFP .
Villagers "wish him a long life", he said.
"They miss him a lot, especially the older ones," he added.
"They hope that he may come back home."
Earlier this month, his friend and renowned human rights lawyer George Bizos, who defended Mandela during his 1960s treason trial, said the ex-president was aware of current political events but was having some trouble with his memory.
"Unfortunately he sometimes forgets that one or two of them had passed on and has a blank face when you tell him that Walter Sisulu and some others are no longer with us," Bizos said.
Sisulu, a former ANC leader who was Mandela's political mentor, died nearly a decade ago.
Last month, two of his granddaughters released a picture of a smiling Mandela sitting with his youngest great-grandson in an armchair.