Four fire engines and around 25 firefighters tackled a fire on High Street North in Manor Park.
Part of a first floor annex at the rear of a three-storey mixed-use building was damaged by fire. Two people left the property before firefighters arrived and there were no reports of any injuries.
The Brigade was called at 1413 and the fire was extinguished by 1457. Crews from East Ham, Plaistow and Barking fire stations attended the scene.
The fire is being treated as accidental and is believed to have been caused by hot works taking place on a flat roof.