WELLINGTON, New Zealand — Forecasts of heavy ocean swells Monday thwarted marine crews trying to pull oil from a leaking ship stuck on a reef off New Zealand's coast, as fist-sized clumps of the fuel started turning up on a popular surfers' beach.
The Liberia-flagged Rena has been foundering since it ran aground last Wednesday on the Astrolabe Reef, about 14 miles (22 kilometers) from Tauranga Harbour, and the government has demanded to know why the ship crashed into the well-charted reef in calm weather.
The ship owner says it is cooperating with authorities in looking into the incident. The 775-foot (236-meter) ship has been leaking fuel, leading to fears it could cause an environmental disaster if it breaks apart.
Marine crews began an operation Sunday to extract up to 1,700 metric tons of heavy fuel oil from the stricken ship – the equivalent of about 10,700 barrels. But they had to halt the pumping Monday after managing to remove just 10 metric tons.
Clumps of the oil were found at Mount Maunganui beach, a favorite spot for surfers, according to Maritime New Zealand, the agency responsible for shipping in the region. The beach is on New Zealand's North Island, about 100 miles (160 kilometers) southeast of Auckland.
The agency believes the ship has another 200 tons of diesel on board. So far, an estimated 30 tons of oil or fuel have leaked into the Bay of Plenty.
Because it's a cargo ship rather than an oil tanker, any spill would be small in comparison to disasters like the 1989 Exxon Valdez spill, which dumped an estimated 262,000 barrels of crude oil in Alaska's Prince William Sound. But because the Rena is close to shore, the oil could still foul delicate estuaries in an area known for its pristine environment.
Maritime New Zealand said that a barge had begun pumping fuel from the stricken ship, but that work was called off to keep crews safe from heavy swells and gale-force winds forecast to hit the area. The operation is expected to last at least two more days once it resumes.
Salvage experts and naval architects are on board to monitor the ship, and sensors should indicate if the ship is in danger of breaking apart, the agency said.
"The top priority is to first remove the oil, then lighten the vessel by removing the containers, and finally, move the ship off the reef," it said.
About 200 people are working on the operation, and New Zealand's defense force has about 300 people standing by in case major beach cleanups are needed.
At least eight sea birds have been rescued from an oil slick that extends about three miles (five kilometers) from the boat.
On Sunday, New Zealand Prime Minister John Key visited the area and demanded answers.
"This is a ship that's plowed into a well documented reef in calm waters in the middle of the night at 17 knots. So, somebody needs to tell us why that's happened," he told reporters.
In a statement, the owners of the ship, Greece-based Costamare Inc., said they were "cooperating fully with local authorities" and were making every effort to "control and minimize the environmental consequences of this incident."
The company did not offer any explanation for the grounding.
The Rena was built in 1990 and was carrying 1,351 containers of goods when it ran aground, according to the owners.
In addition to the oil, authorities are also concerned about some potentially dangerous goods aboard, including four containers of ferrosilicon. Authorities said removing those goods was a priority.