It remains unknown what caused the blaze, but 1,500 campers were forced to leave the campsite from around 2.30am.
Four people suffered minor injuries, including a 5-year-old girl who had inhaled smoke. All were taken to a nearby hospital.
Some 60 firefighters were called in to extinguish the blaze, and it wasn't until around 6.30am on Friday that campers were allowed to return.
The damage was "significant", reported the France Bleu channel, and spread across roughly 500 metres squared.
While many of the campervans escaped serious damage, a handful of mobile homes and cars were totally destroyed, as was some of the island's vegetation.
"The families affected are in total shock," a local firefighter told the channel.
An investigation is underway to determine the cause of the fire.
The island of Oléron, near La Rochelle in western France, is the second largest island of metropolitan France behind Corsica, and is a popular tourist destination.
Photo: Google Maps