US President Barack Obama is due to tour Robben Island - the jail in which Nelson Mandela was kept for 18 years.
The trip comes a day after Mr Obama visited members of the family of the 94-year-old former president, who remains critically ill in hospital.
Mr Obama paid tribute to the impact of the anti-apartheid leader in building a free South Africa, describing him as "an inspiration to the world".
Later, riot police clashed with anti-Obama protesters in Soweto.
Security is likely to be strengthened during this final Cape Town leg of his time in South Africa, says the BBC's Karen Allen who is there.
The US leader did not visit Mr Mandela, but met the Mandela family in private and spoke by telephone to his wife, Graca Machel.
Mr Mandela remains in critical condition. On Sunday South Africa's last apartheid president and the man jointly awarded the 1993 Nobel Peace Prize with Mr Mandela, FW de Klerk, will return to South Africa after cutting short a visit to Europe due to Mr Mandela's poor health.
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