An oil spill in waters off Ecuador's Galapagos Islands which is threatening some of the world's rarest land and sea animals and birds grew worse on Sunday, officials said.

The damaged vessel, the Ecuadorean-registered "Jessica," ran aground last Tuesday half a mile from the archipelago's main port in its easternmost San Cristobal island while its way to service an Ecuadorean navy operation and a private tour boat operator.

The spill has already affected animals including a sea lion, pelicans and several other birds in the islands, administered by Ecuador, and located 600 miles off the coast in the southern Pacific Ocean.

Admiral Gonzalo Vega, director of Ecuador's Merchant Marine in Guayaquil, said Sunday about 144,000 gallons of diesel and bunker, a heavy fuel used by tour boats that operate in the islands, have spilled into the sea. Anywhere up to 96,000 gallons of fuel remain aboard the ship, though crews are working to remove the tanks to avoid future spillage.

"With the movement of the waves, part of the islands' shores have been affected and the rest has gone out to the open sea," Vega told Reuters on Sunday, adding that the boat's incline makes rescuing the fuel even more difficult.

A minor spill began late Friday when a pipe in the ship's machine room burst. But the serious contamination began early Saturday, when strong waves eroded the shipments of diesel and bunker fuel aboard the "Jessica," fouling waters near the islands that boast unique marine and land creatures such as iguanas and giant tortoises.

The global conservation body WWF called Sunday for limits to shipping off Ecuador's Galapagos islands which British naturalist Charles Darwin visited in 1835 developing his theories of national selection.

A statement from the Swiss-based World Wide Fund for Nature warned the spill could have a deep and lasting impact on the creatures of Galapagos.

According to a government report, the spill measures close to 50 square miles, and mainly affects Santa Fe and San Cristobal Islands.

The boat will probably either collapse or split in two, Vega said, though crews are working to remove the tanks of fuel still on board before this happens.

Private fishing operators and Ecuador's marine service have been working since Friday to control the spill, fencing in the fuel and applying chemicals to neutralize its impact.

Local residents tried to prevent the spill from reaching the islands' shores, while the Galapagos National Park Service and Charles Darwin Research Station are struggling to protect threatened wildlife.

EXPERTS ASSESS DAMAGE

One baby lava seagull died, covered in fuel, and a sea lion and several other birds have been affected, Maria Eugenia Proano, representative of the Charles Darwin Scientific Research Station on San Cristobal Island, said on Sunday.

The Galapagos Islands are home to hundreds of species that have evolved for thousands of years in isolation and with little human intervention.

The impact on marine life could not immediately be determined though a spokesman from the Environment Ministry said it was minimal.

A group of experts from the U.S. Coast Guard and Ocean and Atmospheric Administration were scheduled to arrive late Sunday to help remove fuel from the boat.

Robert Bensted Smith, director of the Charles Darwin Research station, said that rescue stations have been set up to aid animals, in case the situation should worsen beyond its present state.

"Until now, the situation has not reached the level of a disaster, but it's very important that they control the spill hopefully today," he told Reuters in a telephone conversation.

The WWF said it was crucial for the Ecuadorean government and the international shipping community to consider designating the waters around these islands as a particularly sensitive sea area.

Sian Pullen, the WWF's widely respected shipping specialist, said such measures would help to ensure a much higher level of protection for this unique area of the world.

Environmentalists have for years feared such an accident off the islands, which lie across shipping routes from the western coast of Central and South America.

They say keeping clear of the islands would add at most only two days to the route south-westwards toward Australia and west toward Indonesia, but that shipping companies have been reluctant to incur the extra cost.