Dozens of firefighters were “working hard” to tackle the blaze, the London Fire Brigade (LFB) said.
At least eleven buses went up in flames at the garage at Farnborough Hill, Orpington.
Locals reported hearing several loud bangs as the vehicles were engulfed in the early hours of Thursday morning, The Telegraph reported.
One wrote on Twitter: “Woken up by 10 huge explosions and what looks like a big fire near Sevenoaks road in Orpington.”
The LFB said it was called to the scene at 3.36am.
“Around 60 firefighters are dealing with a bus depot that is alight on Farnborough Hill, Orpington,” the brigade said.
“Eleven buses are alight and Brigade control officers have taken around 40 calls to the incident which is very visible.
“Firefighters are working hard to tackle the blaze but travel in that area will be difficult due to the number of appliances in attendance, avoid the area if you can.
“Eight fire engines are in attendance from stations including Orpington, Bromley, Sidcup and Biggin Hill.”