Six fire engines and around 40 firefighters were called to a fire at a block of offices and flats on Owen Street in Clerkenwell.
Part of a flat on the fifth floor of a seven-storey block was damaged by the fire. One man left the affected flat and around 40 people left the building before the Brigade arrived. There were no reports of any injuries.
Station Commander Matt Sinclair, who was at the scene, said: "Crews worked hard to bring the blaze under control and fortunately there were no reports of any injuries.
"Firefighters will remain on scene damping down and there is expected to be congestion in the area throughout rush hour."
The Brigade was called at 1536 and the fire was under control by 1652. Fire crews from Islington, Shoreditch, Shadwell, Soho and surrounding fire stations were at the scene.
The cause of the fire is under investigation.