Four fire engines and around 25 firefighters were called to a house fire on Homefield Road in Edgware.
The whole of the first floor and half of the ground floor were damaged by fire in the two storey end-of-terrace house.
One woman jumped from the first floor of the property and was taken to hospital by London Ambulance service.
The property had no working smoke alarms fitted.
A London Fire Brigade spokesperson said: “This incident is a reminder of just how important it is to have working smoke alarms in your home.
“Smoke alarms give the earliest possible warning when a fire starts. We encourage everyone to have smoke alarms fitted in every room where a fire could start, plus a heat alarm in the kitchen. It’s important to test them regularly.”
The Brigade's 999 Control officers received their first call alerting them to the fire at 0158 and the mobilised crews from Mill Hill, Stanmore, Barnet and Hendon fire stations. The fire was under control by 0319.
The cause of the fire is under investigation by the Brigade's fire investigation team and the Met Police.