South Africa's former defence minister and anti-apartheid campaigner Mosiuoa Lekota has died at the age of 77.

He played a key role in the struggle against the racist system of apartheid and was imprisoned on Robben Island alongside former President Nelson Mandela.

Lekota was also a leader of the African National Congress (ANC) before he broke away to form a rival party, the Congress of the People (Cope), citing allegations of corruption in the party which has led South Africa since 1994.

He died after a "period of illness", Cope said in a statement.

President Cyril Ramaphosa paid tribute to the "freedom fighter and a servant of the people".

"His life was one of resilience, courage, and steadfast belief in justice," Ramaphosa said in a statement.

Lekota was one of South Africa's longest-serving ministers, heading the defence ministry for a decade between 1998-2008. 

He also served as the chairperson of the ANC for a decade and was the first premier of the newly-established Free State province after 1994, when South Africa entered a democratic era. 

Lekota, nicknamed "Terror" due to his prowess on the football field, left the ANC in 2008 shortly after former South African President Thabo Mbeki was removed by the party. 

Among his reasons for leaving was disillusionment with how the ANC was governing and mounting allegations of corruption against some of its senior leaders.