Six fire engines and around 40 firefighters were called to a house fire on Coppice Close in Stanmore.
The ground floor of a mid-terraced house was destroyed by the blaze and part of the first floor was damaged. There were no reports of any injuries.
Station Officer Adam Gottlieb, who was at the scene, said: "Crews worked hard in difficult conditions to tackle the fire and stop it spreading to adjoining properties.
"The ground floor was fully alight but their quick work limited the damage as much as possible.
"This incident shows the importance of having smoke alarms - a neighbour was alerted to the blaze after hearing a smoke alarm and seeing smoke coming from the house which prompted them to call 999.
"You should have working smoke alarms in every room where a fire can start, plus a heat alarm in the kitchen and the bathroom. They should be tested regularly."
The Brigade was called at 2152 and the fire was under control by 2335. Fire crews from Stanmore, Harrow and Mill Hill were at the scene.
The cause of the fire is under investigation.