Four fire engines and around 25 firefighters tackled a flat fire on Blackhorse Lane in Walthamstow.
A second floor flat in a seven-storey student accommodation block was destroyed by the fire. Around 150 people left the building before firefighters arrived. There have been no reports of any injuries.
The road was closed and motorists were advised to avoid the area where possible.
The fire is believed to have been accidental caused by a fault within the extractor fan.
A London Fire Brigade spokesperson said: "We'd like to remind homeowners to ensure they don't have dirty ducting. If you don't clean the ducting in your extraction system regularly, you're at a greater risk of a fire.
"You should also make sure you keep the hob, cooker hood and extractor fan clean too – built up fat and grease can ignite and cause a fire."
The Brigade was called at 1457 and the fire was under control by 1610. Fire crews from Walthamstow, Tottenham and Leyton fire stations were in attendance.
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