Six fire engines and around 40 firefighters were called to a house fire on Westwood Road in Barnes.
A loft conversion in a semi-detached house was destroyed by the blaze. Two adults and six children left the property before the Brigade arrived. They were assessed at the scene by London Ambulance Service crews.
Sub Officer Chris Gorbell, who was at the scene, said: “The loft conversion was well alight when crews arrived.
“Firefighters did a brilliant job quickly bringing the fire under control, containing it to the loft and limiting the damage to the rest of the house.
“There were smoke alarms fitted in the property but they weren’t working so the family has been very lucky to get out unharmed.
"Fortunately, one of the occupants woke up and saw the fire so raised the alarm and everyone got out, but we would like to remind people of the importance of having working smoke alarms.
“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, plus a heat alarm in the kitchen.
"They should be tested regularly.”
The Brigade was called at 0616 and the fire was under control by 0702. Fire crews from Richmond, Wandsworth, Fulham, Chiswick, Battersea and Chelsea fire stations were at the scene.
The fire is believed to have been accidental and caused by the incorrect charging of lithium-ion batteries.