The ship has broken in half and an additional 800 tons of fuel oil is believed to be leaking from the front section of the hull, said a spokeswoman with the Royal Society for the Protection of Birds, a British-based conservation group monitoring the situation.

So far, only one salvage vessel has arrived from South Africa, and its spill response and bird rescue capabilities were described as limited. A second, better-equipped response ship is expected to depart for the area from South Africa on Thursday.

Conservation groups said the wreck could pose a different ecological threat to the chain as rats could have come ashore from the vessel, which was carrying 66,000 tons of soybeans from Brazil to Singapore. Several islands in the archipelago are rodent-free, and a rat infestation could potentially do more harm to bird life than any oiling, experts said.