Three people are being treated for smoke inhalation after a blaze broke out at a wooden outbuilding in Adversane this afternoon (Wednesday March 18).
A first floor office in the Stane Street building is reported as being alight.
A female and two males have been given oxygen therapy and were treated by paramedics at the scene for smoke inhalation.
Two fire crews from Horsham and one from Storrington were called to the incident just before 2.30pm.
Four breathing apparatus and four hose reels have been used to tackle the flames.
The outbuilding is used as offices and storage, a spokesperson for West Sussex Fire and Rescue Service said.
Stane Street has been closed both ways due to the fire, affecting traffic between Pulborough and Billingshurst.
The fire has now been extinguished.