The London Fire Brigade said: "Fifteen fire engines and around 100 firefighters were called to a fire near Roxeth Green Avenue in South Harrow.
"The fire occurred at a range of four railway arches, housing businesses including vehicle workshops and other commercial uses.
"The properties have been severely damaged by fire.
"Firefighters have worked hard to bring the fire under control but the Brigade is likely to maintain a significance presence on scene for several more hours."
