Six fire engines and around 40 firefighters were called to a fire at an industrial estate on Weir Road in Wimbledon Park.
Part of a mechanical digger within a single-storey warehouse building was alight. Ten people left the building before the Brigade arrived. There were no reports of any injuries.
Station Manager Justin Coo, who is at the scene, said: "Local traffic control is in place so we are asking motorists to please avoid any unnecessary journeys onto the industrial estate."
The Brigade was called at 0956 and the fire was under control by 1137. Fire crews from Wimbledon, Wandsworth, Tooting, Battersea, New Malden and Mitcham fire stations attended the scene.
The cause of the fire is under investigation.