Asking people to pray for the 94-year-old Nobel Peace Prize laureate, the presidency said Mandela was admitted to the hospital just before midnight yesterday "due to the recurrence of his lung infection", for the third time in four months.
"Doctors are attending to him, ensuring that he has the best possible expert medical treatment and comfort," Presidential spokesperson Mac Maharaj said in a statement.
Maharaj appealed "for understanding and privacy in order to allow space to the doctors to do their work."
He did not identify the hospital, but added that Mandela was "conscious" at the time of admission.
Later, doctors treating Mandela said that the former president was responding "positively" to treatment.
Earlier in March, Mandela spent a night at a Pretoria hospital where he underwent a successful medical examination.
Three months ago, he was admitted for 18 days for treatment of a recurrent lung infection and surgery to extract gallstones. It was his longest stint in hospital since his release from prison in 1990.
Mandela had a long history of lung problems, dating back to the time when he was a political prisoner on RobbenIsland during apartheid. While in jail he contracted tuberculosis.
President Jacob Zuma wished 'Madiba', affectionately referred to by his clan name, a speedy recovery.
"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. We have full confidence in the medical team and know that they will do everything possible to ensure recovery," he said in a statement.
Mandela served as South Africa's first black president from 1994 to 1999 and is widely regarded as the father of the nation for leading the struggle against apartheid and for democracy.
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