Eight fire engines and around 60 firefighters tackled a fire at a butchers shop with flats above on Ilford Lane in Ilford.
Most of the ground floor shop and part of the first floor of the building were damaged by fire. There were no reports of any injuries.
Station Commander Dean Wilkinson, who was at the scene, said: "The fire affected the right hand side of an end-of-terrace shop. One person left the building before the Brigade arrived.
"Crews rescued pet guinea pigs from a flat above the shop.
"One of our 32-metre turntable ladders was used at the scene as an observation tower, providing an aerial view of the incident and helping incident commanders to develop tactics to bring the fire under control."
The Brigade's 999 Control Officers took 10 calls to the blaze.
The Brigade was called at 0316 and the fire was under control by 0505. Fire crews from Barking, Stratford, Plaistow, Ilford and surrounding fire stations attended the scene.
The fire is believed to have been accidental and caused by an overloaded plug socket.