A liquid hydrocarbon spill off the western coast of Corsica poses no serious risk to the coast, a maritime official says.
The spill was probably the result of an uncontrolled discharge on a vessel and is 43km long and one kilometre wide, officials say. It was first spotted by a French customs helicopter.
A maritime official says pollution from the spill poses no serious risk to the coast and was "nothing to fear".
The spill was seen about six nautical miles off the coast and was drifting away, but there were initially fears it could go towards the Scandola Nature Reserve, a UNESCO-listed Heritage Site.
The reserve covers 800 hectares on land and nearly 1,000 hectares at sea. Its waters are incredibly rich in fish, while schools of dolphins can be found just metres from shore.
The exact nature of the contents was not immediately clear, but preliminary information indicated that only 10 to 20 per cent of the spill comprised heavy hydrocarbons, limiting the potential environmental impact.
Two naval tugs had left the southern port city of Toulon and the Corsican capital Ajaccio to help in clean-up operations. The coast off Corsica is rocky, making it difficult to take measures to contain the spill.