Winnie Madikizela-Mandela came to the gates of Mandela's hospital to address crowds, and told them "Tata is sitting up."
"It is true that he is getting better, it is true that he's now sitting on a chair and is able to communicate with the family."
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Cloud and outbreaks of rain will ease away eastwards during the morning, clearing the east coast around midday with sunny spells developing.
Police and emergency services are attending the scene.
Rebel-held east remains at risk while the pumping station supplying the western part of the city is once again in operation.