The fire, which started around 0600 GMT, created a cloud of smoke visible for kilometres (miles) and is still raging, said officials of the Charente-Maritime region.
The four silos on fire are in a row and contain wheat, a spokeswoman for the fire brigade told AFP, adding the fire still risks spreading.
The site and nearby facilities have all been evacuated.
“We are in the process of confirming how many silos are impacted and putting ourselves in a position to protect the other silos,” she added, emphasising there was no immediate indication of an explosion risk.
Nearly one hundred firefighters had been mobilised and “requests for reinforcements” were in progress, the prefecture said.
