"The former president of the ANC and founding president of a free and democratic South Africa is sadly still in hospital, where he remains in a critical but stable condition," Zuma said at a business meeting in Midrand on Wednesday.
"The doctors are doing everything they can to ensure an improvement in his health."
Zuma urged South Africans to continue keeping the elder statesman in their thoughts and prayers. The ailing anti-apartheid icon was spending his 54th day in the Pretoria Medi-Clinic Heart Hospital, where he was admitted on June 8 with a recurring lung infection.
On Wednesday, police were still stationed at both entrances to the hospital and they searched each car before it could enter.
Birthday improvement
Zuma, ministers, the opposition and the public stood united in celebrating Mandela's 95th birthday on July 18.
Presidency spokesperson Mac Maharaj said in a statement earlier that day that Mandela's health was steadily improving.
Thursday July 18 marked Mandela's 41st day in the hospital, where he was being treated for a recurring lung infection.
Defence Minister Nosiviwe Mapisa-Nqakula was also at the hospital, and had a birthday card for Mandela. Mandela's daughter Zindzi Mandela-Motlhajwa said it was encouraging to see signs of recovery. – Sapa