"The Presidency wishes to advise that former President Nelson Mandela is in good spirits and enjoyed a full breakfast this morning. The doctors report that he is making steady progress," President Jacob Zuma's office said in a statement as Mandela was spending a second day in a hospital.
The statement said 94-year-old Mandela "remains under treatment and observation in hospital".
The Nobel Peace Prize laureate was re-admitted to an undisclosed hospital in Pretoria before midnight on Wednesday for the third time in four months.
Earlier this month, Mandela spent a night at a Pretoria hospital where he underwent a successful medical examination.
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Three months ago, he was admitted for 18 days for treatment of the 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 Robben Island during apartheid. While in jail he contracted tuberculosis.
Meanwhile, Zuma said Madiba, Mandela is often fondly known by his clan name, was doing "very well" so far and asked people not to "panic".
"Of course I have been saying to people, you should bear in mind Madiba is no longer that young and if he goes for check-ups every now and again, I don't think people must be alarmed about it. I would like to really say the country must not panic," Zuma was quoted as saying by the BBC.