Four fire engines and around 25 firefighters attended a fire on London Road in Hackbridge.
A range of single-storey building were destroyed by fire. There were no reports of any injuries.
The Brigade received the first of 14 calls about the fire at 1544 and Control Officers mobilised crews from Mitcham, Croydon and Norbury fire stations to the scene. The fire was extinguished by 1650.
The fire is believed to have been accidental and caused by refracted sunlight.
A London Fire Brigade spokesperson said: “Fires caused by refracted sunlight can happen all year round and can be common.
"Our advice is to make sure that you keep mirrors, crystals, glass ornaments and other reflective items out of direct sunlight at all times.”