Nineteen fire crews are now tackling a large blaze at Stamps Hill near Brixton.
The fire includes a combine harvester and corn. It broke out over lunchtime.
Crews are using hose reel jets, main jets, breathing apparatus, a water bowser, multiple beaters and pitchforks.
Local residents and businesses have been advised by the fire service to close all their windows and doors.
Black smoke is being seen for miles around.