Film taken by a French submersible performing a wreck survey has revealed four breaches in the tanker's hull and oil escaping.

Thousands of students pressed ahead with a huge beach cleanup operation as Spain's Deputy Prime Minister Mariano Rajoy did not rule out a new slick wreaking havoc.

Meanwhile, a court in Alaska has reduced the amount of punitive damages imposed on ExxonMobil for the 1989 Exxon Valdez disaster by $US1 billion, however the world's biggest oil company must still pay $US4 billion.

The Exxon Valdez supertanker spilled 11 million gallons of crude oil into Prince William Sound in Alaska in 1989 polluting around 2,000 km of coastline.

Exxon announced immediately that would it launch a fresh appeal.