The first known footage has emerged of South African anti-apartheid leader Nelson Mandela, who as a bearded activist vows to fight racism in a 1956 interview.

The 24-second interview is believed to have been filmed during the 1956-1961 Treason Trial, which ended with the acquittal of Mandela and more than 100 other anti-apartheid activists on treason charges, said the Nelson Mandela Foundation.

Mandela was released in 1991, after spending more than 30 years in prison. He won the Nobel Peace prize in 1993 for his work to promote racial reconciliation in South Africa, and was elected the country's first black president in 1994.

He died in 2013 aged 95, and at his funeral leaders from around the world paid tribute.

In the footage Mandela speaks of his determination to end South Africa's state sponsored system of racial segregation.

"From the very beginning, the African National Congress set itself the task of fighting against white supremacy," Mandela said, referring to the liberation movement that he went on to lead and which has been South Africa's ruling party since the end of apartheid in 1994.

"We have always regarded as wrong for one racial group to dominate another racial group. And from the very beginning the African National Congress has fought, without hesitation, against all forms of racial discrimination and we shall continue to do so until freedom is achieved," a 38-year-old Mandela said.

The Nelson Mandela Foundation said the interview took place at the Old Synagogue in Pretoria, where the Treason Trial was held and was broadcast on January 31, 1961 by Dutch television broadcaster, AVRO.

The earliest filmed interview with Mandela was previously believed to have been conducted in 1961, when he was in hiding. He was incarcerated the following year, and was not released for three decades.