West Sussex Fire and Rescue Service said multiple crews were called to North End Road just before 11.30pm.
Residents in Littlehampton reported on social media last night that they could see ‘massive flames’ all the way from the beach and the loud sound of ‘crackling flames’.
In a post on social media just after 12.10am, a fire service spokesperson said: “We’re currently attending an agricultural building fire.
“Please avoid the area and keep windows and doors closed if you live nearby.”
The fire service said crews from Littlehampton, Arundel, Bognor Regis and Petworth were assisting at the scene.
One jet and one hose reel was still in use at 12.30am.
As of 9.30am, the fire service said one crew from Littlehampton still damping down at the scene. A reinspection is due to take place later this afternoon.