Ten fire engines and around 70 firefighters tackled a blaze at a shop in Leytonstone Road, Stratford.
A small area of the shop, New Local Tools, on the ground floor of the two-storey mid-terraced block of flats was alight
A woman left the building before the brigade arrived and was taken to hospital by London Ambulance crews as a precaution. No injuries have been reported.
A 100-metre cordon has been erected around the site of the fire and Leytonstone Road is closed to traffic.
Station commander Keith Carmichael, who is was the scene, said: “This is a challenging incident because the fire is inside the cavity between the ceiling of the basement and the ground floor of the property.
"Fire crews are breaking into the fascia and walls of the property to access the fire and extinguish it, using thermal imaging cameras and wearing breathing apparatus.
“As fire crews gain access the blaze, thick smoke is escaping. We advise local residents to keep their doors and windows closed.”
The brigade was called at 5pm. Fire crews from Stratford, Leytonstone, Leyton, Plaistow and Homerton fire stations are attending the scene.
The cause of the fire is under investigation by the brigade’s Fire Investigation Unit and the Metropolitan Police Service.
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