The South Africa's presidency has said that former President Nelson Mandela is "unstable" at times but has shown "great resilience" as he remains in a critical condition in hospital.

"Doctors are still working hard to effect a turnaround and a further improvement in his health and to keep the former president comfortable", the office of President Jacob Zuma said in a statement on Saturday.

"His condition tends to stabilise as a result of medical interventions"

Zuma's office also said the president will travel to Malaysia on Saturday on an official visit during which he will receive a peace award on behalf of Mandela.

Mandela, the ailing 95-year-old anti-apartheid icon was rushed to the Pretoria Mediclinic Heart Hospital on June 8 with a recurring lung infection.

Mandela's current hospitalisation is his longest since he walked free from jail in 1990 and went on to become the country's first leader to be elected in all-race elections.

His health has become a concern for South Africa's 53 million people, for whom Mandela remains a potent symbol of the struggle against decades of white-minority rule.

Although it has been relatively quiet outside the hospital where he is being treated, various family members have been visiting him daily.

South Africa's government has been secretive about Mandela's health, issuing infrequent and vague statements and declining to comment on the specifics of his condition.

Source: Agencies