Three fire engines and 14 firefighters and officers attended a grass fire on Mitcham Common on Croydon Road, yesterday.
An area of grass land around three hectares - three times the size of Trafalgar Square, was damaged in the blaze.
A London Fire Brigade spokesperson said: “Grass fires can be started deliberately or accidentally, but however they start, they can cause huge damage to property and kill wildlife. If you see a grass fire, don't attempt to put it out yourself as grass fires can travel very quickly and change direction without warning. Call the fire brigade and let us know where the fire is.
“The most common causes of grass fires are discarded cigarettes, which if thrown from a car window can ignite dry grass verges. Another common way that these fires start is from glass bottles which can concentrate the suns rays onto dry grass and shrubbery."
Firefighters from Mitcham, Purley and Norbury fire stations attended the incident.
The Brigade was called at 1608 and the fire was under control at 1727.