Ten fire engines and around 70 firefighters were called to a house fire on Easebourne Road in Dagenham.
A single-storey lean to was destroyed by the fire and part of the first floor and most of the roof of a semi-detached property was damaged. The roofs of another two neighbouring properties were also damaged by the blaze.
One person was treated at the scene for smoke inhalation by London Ambulance Service crews.
Station Commander John Virtue, who was at the scene, said: "On arrival firefighters were faced with a well developed fire involving three buildings. Crews worked hard to bring the fire under control.
"Firefighters carried out a systematic search of the buildings to ensure that no one was inside.
"The fire started in the roof of one of the buildings and spread to the roofs of neighbouring properties."
The Brigade's 999 Control Officers took 37 calls to the blaze.
The Brigade was called at 1511 and the fire was under control by 1649. Fire crews from Dagenham, Romford, East Ham, Leytonstone, Hainault, Stratford and surrounding fire stations were at the scene.
The cause of the fire is believed to have been a weed burner in the garden of one of the properties which caught light to weeds and spread via fencing and shrubbery and then the buildings.