Videos circulated on social media show huge plumes of smoke emanating from the premises.
Local media reports say firefighters have since been dispatched to the scene and are battling the blaze.
It is believed that at the time of the blaze lawmakers were on Christmas and New Year break.
The main House, the National Assembly, has 400 members. The number of seats that a party has in the Assembly is in proportion to the number of voters that voted for it in the elections.
The National Council of Provinces (NCOP) is the other House of Parliament. The NCOP is constitutionally mandated to ensure that provincial interests are taken into account in the national sphere of government.
Fire at Parliament in Cape Town. Fire marshals now on the scene. @PresidencyZA pic.twitter.com/GQYHxcYk40
— RB (@RoshBardien) January 2, 2022