Four fire engines and around 25 firefighters attended a flat fire on Vicars Bridge Close in Alperton.
Half of a ground-floor flat in a three-storey residential block was damaged by fire. There were no reports of any injuries.
The fire is being treated as accidental and is believed to have been caused by oil overheating in a chip pan.
A London Fire Brigade spokesperson said: "Fires are more likely to start in the kitchen than any other room in the home.
"Cooking should never be left unattended on the hob or grill - if you have to leave the kitchen, turn off the heat.
"Chip pans and cooking with hot oil can be really dangerous and the risk increases when you start frying food more than once.
“All it can take is for you to become distracted for a few seconds and your cooking oil can quickly go up in flames.”
The Brigade received the first of 10 calls at 1458 and Control Officers mobilised crews from Park Royal, Wembley and Ealing fire stations to the scene. The fire was extinguished by 1604.