A city government spokesman says the blaze began early Sunday at the Campofrio plant, where 1,000 employees work, causing an evacuation of the building.
Firefighters were unable to control the blaze, and the highway was closed due to poor visibility after the smoke appeared to cause the collision of a car and truck that left four people injured.
Nearby sports fields and homes also were evacuated.
The plant, which produced ham and sausages, is owned by Campofrio, an international company.
The official spoke on condition of anonymity in keeping with city regulations.