Four fire engines and around 25 firefighters attended a fire at a flat on Wembley Park Drive in Wembley.
A studio flat, situated on the ground floor of a three-storey block of flats, was destroyed by fire.
One person who was inside the flat was treated for smoke inhalation by London Ambulance Service crews. A second person was led to safety from a top floor flat by crews via an internal staircase. Around 20 people left the building before firefighters arrived.
The fire is believed to have been caused by an electrical event in an extension lead.
A London Fire Brigade spokesperson said: “Overloaded sockets are one of the most common causes of electrical fires. Some electrical appliances use more power than others, so be mindful not to overload extension leads and always check that you’re using the right fuse for the plug.
“Power-hungry appliances such as kettles, toasters and microwaves, shouldn’t be on the same extension. It’s also important to fully unwind drum extension leads. If you leave them coiled, they can overheat and cause a fire.”
A smoke alarm was present at the property but did not operate.
“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.
“It is important that you test your alarms regularly to make sure they are in proper working order.”
The Brigade was called at 0948 and Control Officers mobilised crews from Wembley, Willesden and Stanmore fire stations to the scene. A 32-metre turntable ladder was also used at the scene as an observation tower. The fire was extinguished by 1105.