Four fire engines and 21 firefighters and officers dealt with a fire in the roof terrace of a block of flats on the South Bank on Saturday afternoon.
The London Fire Brigade was called to the north block of County Hall at 4.42pm and the fire was under control by 5.33pm.
Smoke was visible from the nearby London Eye.
Firefighters from Soho, Dowgate and Euston fire stations were called to the scene.
A man and a woman left the building uninjured before the brigade arrived.
The cause of the fire is under investigation.