The ANC's headquarters, the Star newspaper and several other buildings in downtown Johannesburg were evacuated on Monday following a bomb scare, an official said.
"Yes, because of the bomb scare at the Star and the [close] proximity of the two buildings [the Star and Luthuli House], the ANC had to request its staff to evacuate the building," said African National Congress spokesman Keith Khoza.
Scheduled meetings were postponed.
Khoza said Sauer Street was closed for about an hour while police combed the Star building.
The nearby housing department and library were also evacuated.
Gauteng police spokesman Colonel Lungelo Dlamini said he had no immediate information and would provide details when they became available.
Reports that Independent Newspaper buildings in Durban and Cape Town were also evacuated could not immediately be confirmed.