Former South African President Nelson Mandela's health is improving daily and he is now able to sit up for minutes at a time, his youngest daughter told state broadcaster SABC.

The 95-year-old has been in a Pretoria hospital for two months for treatment of a recurrent lung infection. The government said late last month his condition remained critical but was showing improvement.

Zindzi Mandela told SABC her father was becoming increasingly alert.

"He's fine. Tata now manages to sit up, like now he sits up in a chair for a few minutes in a day, every day you know he becomes more alert and responsive. Tata is determined not to go anywhere anytime soon, I cannot stress this enough," she said, referring to him by the Xhosa word for father.

"He just doesn't have the strength of a man, he has the strength that is beyond anything that can be explained. Because even now with the challenges to his health, he somehow manages to bounce back when everyone assumes this is the end."

Mandela's victory in the first multiracial elections in 1994 marked the end of the apartheid system. Four years earlier, he was released after 27 years in prison under white minority rule, 18 of them at the notorious Robben Island penal colony.