People continued to drop off messages of support at former president Nelson Mandela's Johannesburg home as the ailing icon entered his sixth day in hospital on Thursday.

Coloured-in drawings of the South African flag were put in the flower beds outside the Houghton home among stones with messages of support.

A card read "Wishing you a speedy recovery Madiba".

Mandela was admitted to a Pretoria hospital in the early hours of Saturday morning due to a recurring lung infection.

The presidency said he was in a "serious but stable" condition. His condition has remained unchanged since then.

President Jacob Zuma told MPs on Wednesday that Mandela was responding "better" to treatment.

Security at the Medi-Clinic Heart hospital remained tight on Thursday, with police officers searching all vehicles entering the facility's two entrances.

A contingent of local and international media has been stationed outside the hospital since Mandela was admitted.

A bouquet of flowers lay next to the entrance with a card reading "Sandu [SA National Defence Union] Loves Madiba".

Some passers-by momentarily stopped to read the message.

Traces of candle wax, from a night vigil held by people wishing the ailing icon well, remained along Celliers Street near one of the entrances to the hospital.

The former statesman's family has been seen at the hospital over the past few days.

On Wednesday, his grandson Mandla Mandela, said the family appreciated the support it had received from South Africans and the global community.

Mandela's wife Graca Machel, and ex-wife and African National Congress MP Winnie Madikizela-Mandela, were seen at the hospital on Wednesday, as well as his daughters Makaziwe and Zenani, and another grandson Ndaba.