Houses on West Avenue and Strand have been evacuated and there are reports of explosions coming from inside the building.
Smoke is visible for miles, people on the scene said, and Route 1 is closed between Route 162 and Plains Road.
Everyone made it out of the building safely and no one has been hurt in the fire, officials said.
Several fire departments are helping extinguish the fire.
The business, located at 46 Erna Ave., makes sheet metal, electronics and more.