Four fire engines and around 25 firefighters were called to a fire at an outbuilding on Harrow Road in Barking.
Most of an outbuilding in a rear residential garden and the garden fencing were damaged by fire. There were no reports of any injuries.
The fire is believed to have been caused by a bonfire which spread out of control.
A London Fire Brigade spokesperson said: "We would urge people to consider if their bonfire is necessary and to take care if you’re burning waste at home.
“Always check your local authority’s advice on bonfires and follow our safety tips.
"Never use paraffin or petrol on your bonfire and make sure you build it far away from any buildings, sheds and fences and never leave it unattended.”
The Brigade was called at 1453 and the fire was under control by 1647. Fire crews from Barking, East Ham and Ilford Fire Stations attended the scene.