The French island of Corsica has launched emergency protocols to contain two oil slicks that were detected 10 kilometres offshore.
Authorities said pollution containing heavy hydrocarbons spanning 19 nautical miles was spotted drifting towards the coast.
Photographs by French navy aircraft, and water samples taken by a local customs vessel confirmed the presence of toxic chemicals.
The Mediterranean Maritime Prefecture said the pollution was probably the result of “degassing”, an operation carried out by oil tankers to ventilate their tanks.
Natural dilution 'impossible'
Because of the size and nature of the chemicals, “natural dilution” was not possible, it said, adding that anti-pollution equipment was necessary.
"The pollution is getting closer to the coast," navy captain Christine Ribbe told BFMTV. “Unfortunately this pollution was already quite close when it was detected."
In a tweet, Ecology Minister Barbara Pompili said the local population had been urged not to touch any cakes of pollution that may be washed up on Corsican beaches, but to instead inform authorities.
Specialised anti-pollution vessels and personnel were being sent to the area Saturday to carry out clean-up operations.