Crews were called to the scene at Lancing Business Park in Chartwell Road.
On its Facebook page, West Sussex Fire and Rescue Service said: “We are currently responding to a large fire involving two industrial buildings at Lancing Business Park in Chartwell Road.
“Please avoid the area and keep doors and windows closed if you live nearby.”
A spokesperson for West Sussex Fire & Rescue Service said: "We received the first of around 50 999 calls at 4.24pm, alerting us to a large fire at Lancing Business Park in Chartwell Road.
"We currently have six fire engines, a water carrier and aerial ladder platform at the scene.
"The fire is involving two industrial buildings and crews are working hard to bring the fire under control.
"Residents are asked to avoid the area and keep their doors and windows closed if they live nearby."
The AA has also put out an alert to drivers on its traffic bulletin.
It said: "Road closed due to building fire on Chartwell Road One Way Street from Marlborough Road to Spencer Road. Traffic is coping well.”
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The firefighters at the scene of the fire. Picture: Eddie Mitchell Photo: EDDIE MITCHELL
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The firefighters at the scene of the fire. Picture: Eddie Mitchell Photo: EDDIE MITCHELL