New Zealand authorities acknowledged Tuesday that the country could be facing its worst maritime environmental disaster in decades as a damaged container ship, trapped off the coast of the Bay of Plenty, remains in danger of spewing tonnes of oil in heavy seas.

Agence France Presse reports that the Liberian-flagged Rena hit reefs near the bay last Wednesday and has since then been unable to move forward while spilling some 350 tonnes of oil.

Maritime New Zealand Director Catherine Taylor told reporters Tuesday that that Rena issued a mayday call, though MNZ officials deployed at the accident site, located some 22 kilometres offshore, filed reports that the ship was in relatively stable condition.

Taylor, however, added that she already ordered for the immediate pull back of the 36-men salvage crew working on the site, citing that "the weather forecast is not good."

"Things are changing all the time, the weather has not worked for us, it's worked against us and we're being precautionary and ensuring we keep people safe first," the MNZ director told AFP.

Initial reports provided by MNZ officials indicated that the Rena sustained damages both on its hull section and its forward holds, where flooding was reported by the ship's crew, a situation that Taylor said may actually help the cripple vessel to gain stability and prevent it from further damaging the reefs underneath.

Also, officials are optimistic that the ship will not break up but covers have been put up on the Rena's fuel tanks as a precaution in the event that it sinks further and reach the sea bed.

MNZ officials say one of the Rena's main tanks was damaged during the reef collision last week and oil leaks that seeped from the ship have reached a significant proportion.

As of Monday, traces of oil have been washed ashore. Shoreline pollution already has killed a considerable number of birds and fish in the beaches straddling the bay area.

As many as 500 dead birds are expected to be collected by wildlife rescue volunteer, and the World Wildlife Fund warned the Bay of Plenty could likely face an environmental disaster.

"The next 24-48 hours are pivotal if an environmental catastrophe is to be averted ... and we are deeply concerned about the threat this oil poses to our marine wildlife, especially seabirds and dolphins," the group said.

WWF noted the Bay of Plenty is a haven for whales, dolphins, penguins, seals and a host of rare sea birds.