South Africa's veteran freedom fighter and Deputy Secretary General of the African National Congress (ANC), Yasmin Jessie Duarte passed away on Sunday after a long battle with cancer. She was 68.

The ANC confirmed that Duarte passed away in the early hours of Sunday morning.

Duarte had been on medical leave since November last year as she underwent treatment for cancer.

She was the longest serving member of the ruling party's national executive council (NEC), after first being elected to the body in 1999 under the leadership of then president Thabo Mbeki.

Sharing its condolences, the ANC said Duarte had been a tower of strength to the organisation as well as a matriarch and pillar of her family.

The passing of Comrade Jessie is a great loss, not only to the family but to the democratic movement and the country as a whole, ANC national spokesperson Pule Mabe said in a statement.

She dedicated her entire life to the struggle for a united, non-racial, non-sexist, democratic, prosperous, and just South Africa. A committed gender activist, she relentlessly championed the emancipation and empowerment of women. Her life and work reflected a consistent commitment to advancing the rights of the poor and marginalised, Mabe added.

As a committed internationalist and former diplomat, not only will she be mourned by South Africa, but by colleagues and comrades on the African continent and the international progressive movement, he said.

A management accountant by profession, Duarte joined the freedom struggle at an early age and was involved in setting up women's structures throughout South Africa while the ANC remained banned in the country under the white minority government.

Duarte served as the personal assistant to Nelson Mandela, who was released after 27 years of imprisonment as a political prisoner to become South Africa's first democratically elected president.

She was also the Member of the Executive Council (MEC) for Safety and Security in Gauteng province and South Africa's ambassador to neighbouring Mozambique for a period.

In April this year, Duarte spoke out after widespread rumours on social media that she had died of cancer. She had earlier indicated that she would step down from her position at the next elective conference of the ANC, scheduled for the end of this year.

Duarte's funeral by Muslim rites was scheduled for Sunday afternoon.

She was married to John Duarte, with whom she had two children. The couple were divorced in 2001.