Sources said at least one arrest had been made, though there are also reports of two attackers, both carrying Islamist flags.
Other sources said that two men rammed the factory in a car before entering and setting off several small explosive devices.
A decapitated body was found nearby the factory, another source said.
The attack came nearly six months after the Islamist attacks in and around Paris that killed 17 people in January.
Those attacks started with a shooting at satirical magazine Charlie Hebdo.
Interior Minister Bernard Cazeneuve said he would go "immediately" to the scene, his office said.
More details coming soon...
