An oil slick was heading towards the French coastline on Thursday after an Italian cargo ship sank in the Atlantic carrying 45 containers of "dangerous materials", authorities said.
The sheet of oil, 10 kilometres long and one km wide, could hit parts of the country's southwest region near the port city of Bordeaux this weekend.
"According to our forecasts, fragments could reach some areas of the coast in Nouvelle-Aquitaine by Sunday or Monday owing to bad weather, which also risks making the anti-pollution operation more difficult," environment minister Francois de Rugy said Wednesday.
France will deploy four ships to help battle the oil slick at sea and will prepare for a clean-up operation on land, he added.
The Grande America was en route from Hamburg in Germany to Casablanca in Morocco when a fire broke out late on Sunday.
All 27 people on board were evacuated the following day as the fire worsened, before the ship sank some 300 km west of the town of La Rochelle on Tuesday.
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"For now the possible pollution risk consists mainly of the 2,200 tonnes of heavy fuel oil on board," Jean-Louis Lozier, head of the regional maritime authority, told reporters in Brest on France's Brittany coast.
Lozier said the hybrid ship's Italian owner Grimaldi had indicated that 365 shipping containers were onboard, "of which 45 are carrying dangerous materials", as well as around 2,000 vehicles.
The fire is thought to have broken out on the car deck before spreading to a container, however the cause is unknown, Lozier said.
"Around forty containers fell into the sea before the ship sank," he said.
"Most of them where badly damaged by the fire." The contents include a hundred tonnes of hydrochloric acid and 70 tonnes of sulphuric acid.
The pollution risk posed by the chemicals "would be very localised", Lozier said, adding most of it would have already burned in the fire.
"Dilution in the ocean would not have serious consequences for the environment." But French environmental campaign group Robin des Bois (Robin Hood) said the group intends to file a complaint at Brest district court over the environmental damage.
"Two thousand vehicles -- it's a car crash at the bottom of the sea, representing hundreds of tonnes of toxic materials in an area very rich in fish, plankton and marine animals," said Jacky Bonnemains, spokesman for the NGO, adding he also feared possible coastal pollution.
Local authorities have opened an investigation and the ship's owner has been warned to "take all necessary measures to contribute to the fight against pollution", the environment minister said.