Six fire engines and 35 firefighters were called to a fire at a supermarket on Winslade Way in Catford last night.
The Brigade was called by quick-thinking neighbours who heard a smoke alarm and dialled 999.
The small fire gutted an electrical intake room on the ground floor and there was smoke damage to the surrounding area.
A spokesperson for the Brigade said: “Thankfully no one was injured in this incident but it shows the importance of having a working smoke alarm. Smoke alarms provide a vital early warning and buy you extra time to escape if there is a fire. As it shows with this case, they can also alert neighbours to the danger of fire.
"Everyone should have at least one smoke alarm on every level of your home and the safest option is have those linked together. This will give the earliest warning if there is a fire in your home."
Firefighters from Forest Hill, Lewisham, Greenwich, Lee Green, Beckenham and Bromley fire stations attended the incident.
The Brigade was called at 0006 and the fire was under control by 0131.