Winnie Madikizela-Mandela, the South African anti-apartheid campaigner and former wife of Nelson Mandela, has died at the age of 81.

A spokesman for her family said that she died peacefully surrounded by her family following a long illness that kept her in and out of hospital since the start of the year.

"She fought valiantly against the apartheid state and sacrificed her life for the freedom of the country," Victor Dlamini said.

"She kept the memory of her imprisoned husband Nelson Mandela alive during his years on Robben Island and helped give the struggle for justice in South Africa one its most recognisable faces."

The nature of her illness was not disclosed.

A crowd of around 200 people soon gathered outside her Soweto home, singing and dancing.

A number of national and local politicians arrived and police closed the street to traffic.

President Cyril Ramaphosa led an outpouring of grief over her death in South Africa.

"Today we have lost a mother, a grandmother, a friend, a comrade, a leader and an icon," said Mr Ramaphosa, who was expected to visit the family home later today.

Retired South African cleric and anti-apartheid campaigner Archbishop Desmond Tutu said: "Her courageous defiance was deeply inspirational to me, and to generations of activists."

Born on 26 September 1936, in Bizana, Eastern Cape province, Ms Madikizela-Mandela became politicised at an early age in her job as a hospital social worker.

After Nelson Mandela was jailed for life in 1964 for sabotage and plotting to overthrow the government, Ms Madikizela-Mandela campaigned tirelessly for his release and emerged as a prominent anti-apartheid figure in her own right, undergoing detention, banishment and arrest.

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She punched the air in the clenched-fist salute of black power as she walked hand-in-hand with Mr Mandela out of Cape Town's Victor Vester prison on 11 February 1990.

For husband and wife, it was a crowning moment that led four years later to the end of centuries of white domination when Mr Mandela became South Africa's first black president.

But their marriage began to fall apart in the years after his release.

The couple divorced in 1996, nearly four decades after they were married. They had two children together.

The end of apartheid marked the start of a string of legal and political troubles for Ms Madikizela-Mandela, as evidence emerged in the dying years of apartheid of the brutality of her Soweto enforcers.

Blamed for the killing of activist Stompie Seipei, whose body was found near her Soweto home, she was convicted in 1991 of kidnapping and assaulting the 14-year-old because he was suspected of being an informer.

Her six-year jail term was reduced on appeal to a fine.