Four fire engines and 21 firefighters and officers were called to a fire at an office block in Saffron Hill, Farringdon.
Around 100kg of insulation materials in a storage room on the ground floor were destroyed by fire.
Approximately 65 people left the building before the arrival of the Brigade. There were no reports of any injuries.
The Brigade was called at 1056 and the fire was under control at 1350. Fire crews from Shoreditch, Soho and Dowgate fire stations attended the scene.
The cause of the fire is under investigation.