Anti-apartheid icon Nelson Mandela, although still serious, has made "sustained" improvement in health condition and is engaged with his family, South African President Jacob Zuma said today.

"Over the last two days, although he (Mandela) remains serious, his doctors have stated that his improvement has been sustained. He continues to engage with family," Zuma said as 94-year-old Mandela spent his 9th day in hospital battling recurrent lung infection.

Addressing the commemoration of National Youth Day at Newcastle, KwaZulu-Natal, the South African President asked the audience to keep Madiba (Mandela's clan name) in their thoughts and prayers.

"As you are aware, President Nelson Mandela is still in hospital in Pretoria," Zuma said.

"We are grateful that he continues to get better," he said, while wishing Mandela a "very happy Father's Day".

"We love him and know that he loves us too," Zuma said.

Mandela was admitted at the Mediclinic Heart Hospital in Pretoria last Saturday after he suffered from a recurrent lung infection. This was his fourth hospitalisation since December.

Yesterday, a grandson of the anti-apartheid hero had said that Mandela seems to be on the road to recovery from a recurrent lung infection after visiting him in hospital.

Mandla Mandela said his grandfather "looked good" when he visited him in hospital along with two elders. "It gave us hope that he is going to recover soon," he said.

Mandela had a long history of lung problems, dating back to the time when he was a political prisoner on Robben Island during apartheid. He contracted tuberculosis in 1988 during his 27 years in prison.

In December, he was admitted for 18 days for treatment of the lung infection and surgery to extract gallstones. It was his longest stint in hospital since his release from prison in 1990. In March, he was admitted for an overnight scheduled check-up before returning that month for 10-days.

Mandela, one of the world's tallest statesmen, led the movement to replace the apartheid regime of South Africa with a multi-racial democracy. He won the Nobel Peace Prize in 1993. Mandela served as president from 1994 to 1999.

Though Mandela retired from public life in 2004 and has been rarely seen in public since 2010, he remains a towering symbol in South African public life.