A West Sussex Fire and Rescue spokesman said the initial call came in at 4.09pm about a fire in the road.
“Crews attended and are still there now,” he said, adding that police have closed the road between the two roundabouts.
He said there is an officer in attendance and that the fire service has two engines at the scene.
“Initially they thought it was a gas pipe but they actually think it now might be more electrical so we’ve requested both gas and UK power so they can both come and assist,” he said.