Part of an electrical intake cupboard in a storeroom was damaged by fire. Two people left the building before the Brigade arrived. There were no reports of any injuries.
The fire was discovered by a member of staff who heard a bang and saw fire in the storeroom.
The Brigade was called at 7.40am and the fire was under control by 8.06am. Two fire engines from Sidcup and Eltham fire stations attended the scene.
The fire is believed to have been accidental and involved an electrical meter.