Four fire engines and 25 firefighters were called to a house fire on Millfield Avenue in Walthamstow.
Most of the ground floor and part of the first floor were destroyed by fire. One woman was treated on scene for smoke inhalation by the Brigade and London Ambulance Service. Two children evacuated the property before the Brigade arrived.
Fire investigators believe there were no smoke alarms in the property.
A London Fire Brigade spokesperson said: “This incident shows just how important it is to have working smoke alarms fitted on every level of your home.
“Smoke alarms give the earliest possible warning when a fire starts and we would urge everyone to make sure they have one fitted in every room where a fire can start except kitchens or bathrooms where heat alarms are more appropriate.”
The Brigade's 999 Control operators received a call about the fire at 1630 and deployed fire crews from Walthamstow, Leyton and Chingford fire stations.
The cause of the fire is accidental.