The roof area had caught fire and the part of the complex where the National Assembly (lower house) meets was on fire too, the city authorities initially said.
Minister of Public Works, Patricia de Lille, later said the fire in the Chamber of the Council of Provinces (the parliament’s upper house) had been contained, but the National Assembly was still burning.
Images show a plume of black smoke filling the sky, with huge flames coming out from the roof of the building. Dozens of firefighters are at the site battling the blaze; it is not yet clear what caused the fire.
It comes hours after Archbishop Desmond Tutu’s state funeral at St George’s Cathedral, near parliament.
The Houses of Parliament in Cape Town are made up of three sections, with the oldest dating back to 1884. The newer sections built in the 1920s and 1980s house the National Assembly.