Johannesburg Emergency Services spokesperson Nana Radebe told News24 that paramedics were on scene.
Tweets from Independent Online confirmed that a body lay on the pavement next to the building.
Radebe said the building was evacuated after the fire broke.
Further details were not immediately available.
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Newsdeck
Firefighter falls from upper floor of govt building while battling blaze
A firefighter fell from the upper floors of a government building in the Johannesburg CBD while battling a blaze there on Wednesday morning.
