Spanish media have reported that an oil slick estimated at 800 square km (309 square miles) was encroaching on the northwest coast.

Previous slicks from the Prestige, which broke in two and sank on November 19, have soiled hundreds of kilometres of coastline in the region of Galicia, creating Spain's worst ever environmental disaster.

Rich fishing and shellfish grounds have been inundated by the foul-smelling sludge, putting thousands of people in fishing related industries out of work.

Experts studying the wreckage with the help of the French mini-submarine Nautile say about 20,000 tonnes of the total 77,000 tonnes that were on board have leaked into the sea.

"I have here the reports written by several authorities (from Portugal and France) that it (the slick) is moving towards the north because there is a very strong wind from the south and so it is moving away from the coast," Rajoy told reporters in the Galician city of La Coruna.

Forecasts suggested more stormy weather was due to hit the area, further complicating clean-up efforts.

In addition to a fleet of specialised ships, thousands of military personnel, state workers and volunteers were at work scrubbing fuel oil off the rocky beaches of Galicia.

The Christmas season is normally a bonanza for the local fishing industry but much of the fleet is now grounded, leaving thousands at the mercy of government aid.

The wreckage of the Prestige rests on the ocean floor some 3.5 km beneath the surface, about 130 nautical miles from the mainland.

Rajoy said the Nautile has covered three of the 14 cracks in the hull to try to stem the leakage of about 120 tonnes of fuel oil per day from the bottom of the ocean.