A spoksman for West Sussex Fire and Rescue Service said crews were called to Mill Pond Way just after 11am to reports of a property on fire.
Three engines from East Preston, Littlehampton and Worthing all arrived to find a fire in the first floor of the house.
Crews wearing breathing apparatus quickly got to work on extinguishing the fire with two high pressure hoses and a covering jet, as well as a hydrant.
All residents have been accounted for, the spokesman said, and the fire has been extinguished. Firefighters are still at the scene damping down.
The spokesman added: “We would urge members of the public to avoid the area for the time being, and residents living nearby should keep their doors and windows closed.”