Four fire engines and 21 firefighters and officers were called to a grass fire in Hockenden Lane in Swanley.
Approximately two hectares of crops and grass were destroyed by fire.
A London Fire Brigade spokesperson said: "During the hot weather we are attending a large number of grass fires across London.
"We’re asking the public to take care not to drop cigarettes or matches on dry grass and to keep a very close eye on barbecues.
"Dropped glass can also start fires as the sun can magnify the sun’s rays.
"Grass fires can quickly spread and cause serious damage, so if you see grass smouldering, please call 999 immediately.”
• Never leave camp fires or barbecues unattended and extinguish them properly after you have finished using them
• Clear away bottles, glasses and any broken glass to avoid them magnifying the sun and starting a fire
• Dispose of smoking materials such as cigarettes safely
• Explain to children the dangers of playing with and lighting fires
The Brigade was called at 1024 and the fire was under control at 1137. Fire crews from Sidcup and Orpington fire stations attended the scene.