Johannesburg — Former president Nelson Mandela has been re-admitted to an undisclosed hospital, the presidency said on Thursday morning.
He was hospitalised on Wednesday before midnight due to a recurrence of his lung infection, spokesman Mac Maharaj said in a statement.
"Doctors are attending to him, ensuring that he has the best possible expert medical treatment and comfort."
President Jacob Zuma wished him 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," Zuma said in the statement.
"We have full confidence in the medical team and know that they will do everything possible to ensure recovery."
Maharaj appealed for "understanding and privacy in order to allow space to the doctors to do their work".
Earlier this month, Mandela was admitted to a Pretoria hospital for a scheduled check-up. He was discharged the following day.
In December, Mandela underwent an operation to remove gallstones and to treat the recurring lung infection. He was discharged after an 18-day stay and placed under home-based high care at his Houghton, Johannesburg, residence.
In January, the presidency said Mandela had made a full recovery from the surgery and continued to improve.
In February 2012, he was admitted to hospital for a stomach ailment. At the time, the presidency said Mandela underwent a diagnostic procedure to investigate the cause of a long-standing abdominal complaint.
In January 2011, Mandela was taken to Milpark Hospital for routine tests relating to respiratory problems.
Mandela's last major public appearance was in July 2010, at the final of the Fifa World Cup at Soccer City stadium in Johannesburg.
Since then he had spent his time between Johannesburg and his ancestral village of Qunu in the Eastern Cape.
South Africa's first black president 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.