Twelve fire engines and around 80 firefighters tackled a fire on Imperial Way in Croydon.
Part of a single-storey warehouse, with an office block attached, was alight.
Imperial Way is closed.
One of the Brigade's 32-metre turntable ladders was used to provide an aerial view of the fire.
The Brigade was called at 0636 and Control Officers mobilised crews from Croydon, Purley, Norbury, Addington and Mitcham fire stations to the scene. The fire was under control by 1050.
The cause of the fire is under investigation.