The Italian ship was carrying dangerous substances including hydrochloric acid and sulfuric acid.
There was an oil leak trying to contain four French vessels to expand, in addition to land preparations.
An oil spill of 10 kilometers and a kilometer could reach parts of the French southwestern coast near Bordeaux.
"We expect parts of some of the coastal areas of Novell Aquitaine to be reached soon because of the poor weather, which also threatens to make the cleaning process more difficult," said Environment Minister Francois de Rugi.
The ship was on its way from Hamburg, Germany to Casablanca in Morocco when a fire broke out on board.
All 27 people aboard were rescued the next day as the fire raged before the ship sank about 300 km west of La Rochelle.
"At present, the potential pollution risk is mainly related to 2,200 tons of heavy oil on board," Jean-Louis Lozier, head of the regional navigation department, told reporters in Brest on the French coast of Brittany.
Adding that the ship's owners Grimaldi indicated that 365 containers were aboard the ship "45 of them contain dangerous materials" in addition to about 2000 vehicles.
The fire was believed to have arisen on the deck of the car-laden ship before it could be carried into a container but without knowing the cause, Luzier said. "About 40 containers fell into the sea before the ship sank," the majority of them were severely damaged by the fire, according to the minister.
The contents of these containers are 100 tons of hydrochloric acid and 70 tons of sulfuric acid.
Local authorities have opened an investigation and ship owners have been warned to "take all steps to contribute to pollution control," according to the environment minister.