Spain has contracted a French firm which owns the specialised Nautile mini-sub - best known for discovering the wreck of the Titanic - to seal up the oozing ship.

After plugging one leak last week, the sub was being transported back to the wreck site by another ship on Wednesday and was due to dive on Thursday.

High pressure and cold 3,600 metres (two miles) under water where the Prestige lies present unprecedented problems.

The project will cost around 1.2 million euros (dollars) according to Emilio Lora-Tamayo, a leading member of a scientific committee set up to solve the crisis.

Bunging the holes will take up to 20 dives, but even after the cracks are sealed the vessel may continue to leak oil.

"The estimate is that in the worst case there could be remaining leaks...to the order of 11 tonnes (a day)," he said.

The Nautile will shove metal bells into gaping holes, cover other gaps in sheeting and for smaller cracks, will use bags filled with metal balls.

Its job was likely to be done by January 20, allowing for rough weather off the rugged Galician coast.

Meanwhile, Lora-Tamayo's research committee will continue to work on a permanent solution for a disaster.

Earlier, environmental activists Greenpeace said the fuel oil from the Prestige contained toxins which were fat soluble and could remain in the human body for years, possibly causing cancer, if passed on through the food chain.

It said the environment would not recover from the spill for 10 years.

"Judging by other slicks...we're talking about a decade at least...not simply for fish or barnacles to come back, but for the ecosystem to regain its balance," Maria Jose Caballero, head of Greenpeace's coastal campaign, told reporters.

She said in France after a similar oil spill from the tanker Erika in 1999, many sea birds were left sterile.

Spain says it had spent 200 million euros so far offsetting damage from the spill.

Prime Minister Jose Maria Aznar said on Saturday regions whose fishing industry has been devastated by oil from the Prestige will receive 265 million euros of European Union funding.