Former South African President Nelson Mandela is responding "positively" to treatment after he was admitted to hospital with a recurring lung infection, according to a statement released by President Jacob Zuma's office.
The 94-year-old was admitted to hospital to hospital in Pretoria just before midnight and remains "under treatment and observation".
Africa Correspondent Rohit Kachroo reports:
South Africa's presidency said that doctors were acting with extreme caution because of the advanced age of the anti-apartheid leader, who has become increasingly frail in recent years.
In December, Mandela spent three weeks in a hospital in Pretoria, where he was treated for a lung infection and had a procedure to remove gallstones.
Earlier this month, he was hospitalised overnight for what authorities said was a successful scheduled medical test.
Mandela has been particularly vulnerable to respiratory problems since contracting tuberculosis during his 27-year imprisonment for fighting white racist rule in his country.
Presidential spokesman Mac Maharaj, referring to Mandela by his clan name Madiba, said the latest stay was not for previously planned treatment.
No, this wasn't scheduled. As you will appreciate the doctors do work with a great sense of caution when they are treating Madiba and take into account his age.
And so when they found that this lung infection had reoccurred, they decided to have him immediately hospitalized so that he can receive the best treatment.
President Zuma wished Mandela 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.
There has been a global outpouring of messages expressing concern for Mandela's health.