Four fire engines and around 25 firefighters tackled a fire at a block of flats on Headstone Road, in Harrow.
Part of a four roomed flat on the fourth floor of the nine storey building was damaged by the fire. Around 42 people were evacuated from the building. One man was treated on scene by London Ambulance Service.
The fire is being treated as accidental and believed to have been caused by the unsafe use of incense sticks.
A London Fire Brigade spokesperson said: "Incense sticks, candles and oil burners are one of the most common causes of fire within homes. It’s really important that you never leave these items unattended.
"Make sure you place incense sticks in a suitable, fire-resistant holder and keep them away from curtains and anything else that can easily catch fire. Remember to put them out entirely when you leave the room and especially before bed."
Control Officers took the first of 10 calls at 0624 and mobilised crews from Harrow, Northolt, Wembley and surrounding fire stations to the scene. The fire was extinguished by 0747.