PRETORIA - Rival South African opposition parties joined forces on Wednesday when tens of thousand demonstrators marched through the capital Pretoria calling for President Jacob Zuma to resign.

The march to Union Buildings, the official seat of government, was organised on Zuma's 75th birthday and came after nationwide rallies against the president last week.

Zuma's recent sacking of respected finance minister Pravin Gordhan has fanned years of public anger over government corruption scandals, record unemployment and slowing economic growth.

Supporters of the radical leftist Economic Freedom Fighters (EFF), the main opposition Democratic Alliance (DA), and smaller parties mingled at Wednesday's demonstration in a display of unity.

Police said the event had been peaceful. "You came out in large numbers and sent a strong message," EFF leader Julius Malema told the crowd.

"We are here to defend the future of our children whether you are black (or) white. We are united on the purpose of winning back our beautiful country."

Gordhan's sacking triggered unprecedented criticism from senior figures within the ruling African National Congress (ANC), including from Deputy President Cyril Ramaphosa.