Fire engines have been sent to the scene from Bognor, Chichester, Littlehampton, Worthing, Arundel, Havant, Midhurst and East Preston.
West Sussex Fire and Rescue Service said crews are using breathing apparatus, hose reels and an aerial ladder platform at the retail store.
There are no reported injuries.
It is understood the fire broke out in Keith Jay Carpets and Furniture Shop at 66-68, London Road, Bognor around 7pm.
Updates to follow.
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