Four fire engines and around 25 firefighters were called to a fire at a row of terraced houses on Northumberland Avenue in Hornchurch.
Hornchurch Watch Manager Alan James, who was at the scene, said:
"We believe the fire started when electric cables under the wooden decking became overheated.
"When we arrived the flames were giving the sky an orangey glow and the crews worked hard to stop the fire spreading to further properties.
A small part of the ground and first floor of one property was damaged by fire. The blaze also affected the rear and back gardens of two adjacent houses. There were no reports of injuries.
The Brigade was called at 2134 and the fire was under control at 2259. Fire crews from Hornchurch, Harold Hill, Romford, and Ilford fire stations attended the scene.