South Africa's ailing anti-apartheid icon Nelson Mandela may have to stay in hospital over Christmas, a presidential aide suggested on Sunday, although he declined to give any update on his current state of health.

The frail 94-year-old former president was admitted to hospital in the capital Pretoria on December 8. He is receiving treatment for a recurring lung infection and has also had a procedure to remove gallstones.

"We all wish that he could be home for Christmas, but first and foremost he needs to get better," presidential spokesman Mac Maharaj told AFP after press reports he may stay in hospital during the festive season.

"At this stage there is no update on his condition and his doctors have given no indication about when Madiba will be discharged," Maharaj said, using Mandela's clan name.

Only President Jacob Zuma's office is tasked with issuing updates about the health of the revered elder statesman.

Official reports about his treatment have not revealed much information about the seriousness of Mandela's condition nor details about the sort of treatment he is undergoing.

Mandela used to throw lavish Christmas parties for children in his southern rural home village of Qunu, where kids from impoverished backgrounds would be showered with gifts.

American talk show host Oprah Winfrey, who is a close friend of Mandela, attended a party in 2002.

But the events ceased after he retired from public life in 2004 and since then he has been spending Christmas privately with his family.

Local and international journalists have been camping outside Mandela's suburban home north of Johannesburg since the beginning of the week as rumours of an imminent release from hospital made the rounds.

A government official initially said Mandela was being cared for at the One Military hospital outside Pretoria, the country's top military facility. Press reports later said he was at the private Mediclinic Heart Hospital in the capital, but this has not been confirmed by the government.

Radio 702 reported that security is tight outside the Mediclinic.

Zuma visited Mandela on Saturday and but did not reveal details about his condition except to say that he was "responding to treatment".

Zuma had told delegates at the end of the ruling ANC's party conference on Thursday that the Nobel Peace Prize laureate's condition was serious when he was admitted to hospital but said he was a fighter.

"Madiba is an unparalleled fighter and has always been so. He has met all his health challenges with his tremendous fortitude and grace".

This is the longest time Mandela has spent in hospital since being released from prison in 1990 after 27 years.

He was previously hospitalised for an acute respiratory infection in January 2011, when he was kept as an inpatient for two nights.

He became South Africa's first black president in 1994 after the end of apartheid, and stepped down in 1999 after spending one term in office.