"Doctors advise that due to the lung infection former President Mandela had developed a pleural effusion (excess fluid in the lungs) which was tapped," Presidential spokesperson Mac Maharaj said. "This has resulted in him now being able to breathe without difficulty. He continues to respond to treatment and is comfortable, the statement said.
"Former president Nelson Mandela was admitted to hospital during the late hours of 27 March due to a recurrence of pneumonia," it said.
The Nobel Peace Prize laureate was previously said to be re-admitted to a hospital in Pretoria for a recurring lung infection for the third time in four months.
After he was admitted to the hospital, President Zuma had said Madiba (Mandela is often fondly known by his clan name) was doing "very well" so far and asked people not to "panic".
The president office had said on Friday that Mandela was in "good spirits" and making "steady progress". "The presidency wishes to advise that former president Nelson Mandela is in good spirits and enjoyed a full breakfast this morning," the statement had read.
The presidential spokesperson has thanked media and the public for their cooperation in respecting the privacy of Mandela and his family.
Earlier this month, 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 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. He contracted tuberculosis in 1988 during his 27 years in prison.
Mandela still in hospital, making 'steady progress'
Nelson Mandela 'responding positively' to treatment
Nelson Mandela back in hospital with lung infection
Pistorius set to receive snub from major athletic events
'Being Indian is like having the right visiting card'