Eight fire engines and around 60 firefighters were called to a fire on Ladbrook Close in Pinner.
The fire involved three bungalows. Two of the bungalows were partially damaged whilst a third bungalow's roof was destroyed in the fire.
One person was assessed at the scene by London Ambulance crews.
The Brigade received the first of 20 calls reporting the fire at 1538 and Control Officers have mobilised crews from Northolt, Ruislip, Stanmore, Wembley and Hillingdon fire stations to the scene. A 32-metre turntable ladder was also in attendance. The fire was extinguished by 1854.
The cause of the fire has been recorded as accidental.