President Jacob Zuma made "unmatched sacrifices" to liberate South Africa, the African National Congress (ANC) said in its birthday wishes to him on Wednesday.

Zuma celebrates his 75th birthday on the same day as that of former finance minister Pravin Gordhan, who turns 68. Zuma fired Gordhan during his massive and controversial Cabinet reshuffle on March 30.

Since then, two credit ratings agencies have downgraded South Africa to junk status.

Thousands of South Africans, representing several opposition political parties, on Wednesday staged a second march to the Union Buildings to demand that he resign as head of state.

ANC spokesperson Khusela Sangoni said in a statement that the party was grateful to Zuma and other freedom fighters.

"The president has been at the forefront of the efforts to build a national democratic society underpinned by radical socio-economic transformation characterised by inclusive growth and a better life for all our people."

She said Zuma had committed himself to expediting land redistribution, eradicating racism, and building social cohesion and unity.

"The ANC wishes President Jacob Zuma many happy returns and a happy and productive day."

The ANC is expected to celebrate his birthday at the Walter Sisulu Square of Dedication, in Kliptown, Soweto, at 15:00 on Wednesday.