The fire started on a conveyor belt at around 8:00 a.m. (0600 GMT) and spread to four grain silos operated by SICA Atlantique, the local prefecture said.
Staff from SICA Atlantique and neighbouring companies in the terminal were evacuated and no injuries were reported, it said.
The fire had been brought under control and had not reached compartments containing stored grain, a representative of SICA Atlantique said.
France is the European Union's biggest grain producer and the cereal terminal at La Rochelle, known as La Pallice, is an important export outlet as it handles larger panamax vessels.
Comment: Footage of the fire:
A major fire is underway near the commercial port of La Rochelle in a grain silo which stores several thousand tonnes of wheat. There is a risk of spread and explosion according to France Bleu. #LaRochelle
The port has loaded a large amount of barley for China this summer as the harvest has arrived, though the current loading schedule was light, according to port data compiled by Refinitiv.
Comment: So, it doesn't sound like the port was under any particular pressure with regards to the size or timing of these particular shipments, however that they were intended for China is notable.
Cereal loading activity had been suspended at La Pallice due to the security zone established by firefighters, two shipping sources said.
La Rochelle port referred queries to the local prefecture.
Comment: This incident in France, that comes on the heels of the explosions at grain silos in Turkey (just a few days ago), and Brazil (2 weeks ago), serve as support for the theory that, as with the highly suspect food plant fires that began in earnest in the last 2 years, these incidents at grain silos might be part of a concerted effort to disrupt the already highly vulnerable food supply: Explosion at grain silos at Turkey's Derince port, several injured
A selection of the food plant fires in the last year or so: