The American captain of a giant cruise liner is standing trial in Marseille on charges of breaching pollution limits in the first such case in France amid rising concerns over the smog threat from such massive tourist ships.

The unprecedented trial opened as maritime authorities battled a vast oil slick off Corsica after a cargo ship rammed into another freight vessel near the French Mediterranean island early on Sunday.

Evans Hoyt, 58, has been charged with burning bunker fuel containing 1.68 per cent sulphur - above the European limit of 1.5 per cent. Mr Hoyt was prosecuted after a spot check on his ship Azura - a liner of up to 3,000 berths and one of the largest in the fleet of P&O Cruises, whose parent company Carnival is also being charged.

He faces up to one year in prison and a €200,000 (£176,000) fine.

Tracked down by investigators a few days after the testing during a stop east of Marseille, the captain - not present in court - has admitted using the fuel.

In court, his lawyer, Bertrand Coste contended that European environment rules unfairly distinguished between cruise ship limits and those for cargo vessels, which is higher, saying this meant there was a lack of "equality before the law". He also sought to have the trial annulled due to alleged procedural errors.