Nelson Mandela is not in any danger after his hospitalisation today and should be released within two days, South African President Jacob Zuma said.

"We are happy that he is not in any danger and thank the doctors for their hard work and professionalism. He is receiving good medical care and is expected to be discharged from hospital either tomorrow or Monday," Zuma said in a statement.

"Madiba is fine and fully conscious and the doctors are satisfied with his condition, which they say is consistent with his age," Zuma said, referring to Mandela by his affectionate clan name.

"He was in good health before admission in hospital but doctors felt the complaint needed a thorough investigation. He underwent a diagnostic procedure as part of his ongoing medical management."

Zuma's office said earlier that Mandela has been admitted to hospital for a long-standing abdominal complaint, but relatives and officials have rushed to reassure the nation that his overall health is good.