In videos on social media, the double-decker was seen billowing smoke in Streatham Hill.
The London Fire Brigade (LFB) has since released a statement saying the driver and passengers left the bus.
The LFB added there were no injuries from the incident which unfolded at 9.50am and the fire was under control by 10.22am.
A statement read: “Firefighters have dealt with this bus fire in Streatham Hill.
“The driver and passengers left the bus before the Brigade arrived. There are currently no reports of any injuries.
“The Brigade’s 999 Control Officers took 19 calls to the blaze.
“The Brigade was called at 0950 and the fire was under control by 1022. One fire engine from Brixton Fire Station attended the scene.”
A witness to the incident posted an image on Twitter, accompanied by the caption: “Well this is frightening!
“Bus in Brixton pulled into the stop and promptly caught on fire. Huge flames & crashing as bits of it were burned off.”