Former South African President Nelson Mandela is “responding positively” to treatment for the recurrence of a lung infection, the presidency says.
A statement said the 94-year-old anti-apartheid leader remained under treatment and observation.
Mr Mandela was admitted to hospital just before midnight, the office of President Jacob Zuma said earlier.
He spent 18 days in hospital in December undergoing treatment for a lung infection and gallstones.
In an update on Mr Mandela’s condition, the presidency statement thanked the media and the public “for their co-operation in respecting the privacy of Madiba [Mr Mandela] and his family”.
Mr Mandela is regarded by many South Africans as the father of the nation for leading the struggle against apartheid.
He served as South Africa’s first black president from 1994 to 1999. However, his health has caused concern for some time.
Earlier, a presidential spokesman told the BBC that Mr Mandela was conscious in hospital.
“I think we need to be clear that the doctors are attending to Madiba [Mr Mandela] on a continuous basis,” spokesman Mac Maharaj said.
“They prefer to act on the side of caution, and the moment they felt there was a recurrence of the lung infection, they felt that it warranted immediate hospitalisation given his age and given his history.”