French environment minister Francois de Rugy has slammed the "abnormal actions" of a Tunisian ro-pax that hit an anchored boxship off Corsica on Monday.
The 17,900-gt Cotunav ferry Ulysse (built 1997) steamed into Cyprus Sea Lines' 5,018-teu CSL Virginia (built 2005) on Sunday, spilling 600 tonnes of fuel in a slick stretching for miles.
French and Italian civil and military teams were working to contain the spead of the oil.
De Rugy told reporters that officers from France's paramilitary police had been airlifted to the ships to investigate the incident, but it was too early to say what had happened, he added.
The ferry was en route from Genoa to Rades in Tunisia.
CSL Virginia was not carrying any cargo.
Italian anti-pollution vessels have begun pumping the slick, Rugy added, according to The Local website.
The spill is said to be moving away from Corsica.
"The first priority is to extricate the two boats," Rugy said, adding the operation was "very complicated".
Video footage showed the front of the ferry embedded inside the hull of the boxship.
A simulation using AIS data by MarineTraffic shows the ferry maintaining a straight course and ploughing into the boxship at 19 knots.
A criminal investigation has been launched into the pollution, Marseille prosecutor Xavier Tarabeux said.
Corsica leader Gilles Simeoni said he was determined to find out what caused the accident, which occurred in relatively calm seas with good visibility.
CSL and Cotunav have been contacted for further information.
