West Sussex Fire and Rescue Service said crews were alerted just after 12pm to reports of a property on fire in Aldwick Place.
A spokesperson added: “Joint Fire Control mobilised fire engines from Bognor Regis Chichester, Littlehampton and Selsey to the scene along with Hampshire & Isle of Wight FRS crews from Emsworth and Havant.
“The Aerial Ladder Platform from Worthing has also been sent to the scene along with the Incident Command Unit from Haywards Heath.
“Firefighters wearing breathing apparatus are using three hose reels and a covering jet to extinguish the fire.
“We would urge residents living nearby to keep their doors and windows closed, and would encourage drivers to avoid the area for the time being to allow our crews to work safely.”
In an update at 4.20pm, the fire service said the incident has been scaled back.
“We now just have one crew from Bognor Regis Fire Station in attendance at the scene,” the spokesperson said.
“Fire investigation officers are currently on scene to establish the cause of the fire.
“We would like to thank residents for their patience while this incident was brought under control.”