WELLINGTON, New Zealand (AP) — Small amounts of oil from a container ship stuck on a reef for days began washing up at a popular New Zealand beach on Monday, while work to extract oil from the vessel was called off because of weather concerns.

The Liberia-flagged Rena struck the Astrolabe Reef about 14 miles (22 kilometers) from Tauranga Harbour early Wednesday, and has been foundering there since. The 775-foot (236-meter) ship has been leaking fuel, leading to fears it could cause an environmental disaster if it falls apart.

After beginning an operation Sunday to extract up to 1,700 metric tons of oil from the stricken ship, marine crews halted the pumping Monday after managing to remove just 10 metric tons.

New Zealand Ship Grounding

The Liberian-flagged container ship MV Rena is stuck hard aground on a reef 12 nautical miles off the coast of Tauranga, New Zealand. Pic: AP.

Fist-sized clumps of 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 agency believes the ship has about 1,700 metric tons of oil and 200 tons of diesel on board. So far, an estimated 30 tons have leaked into the Bay of Plenty, a spot noted for its fishing, diving and aquatic wildlife.

Heavy swells and gale-force winds were forecast to hit the area on Monday and last for a few days.

The agency said that a barge, the Awanuia, had begun pumping fuel from the stricken ship, but that work was called off in order to keep crews safe. The operation is expected to last at least two more days once it resumes.

“The weather is expected to deteriorate in the coming days, so we are working around the clock to remove the oil,” the agency said in a statement.

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.

A navy vessel, the Endeavour, will be used as a command platform for the operation. 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.

So far, at least eight sea birds — six little blue penguins and two shags — 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.

Environmental agency Greenpeace denounced the spill and what it claims is a slow response.

“This is an unfortunate illustration of just how difficult it is to deal with oil spills at sea,” said Greenpeace spokesman Steve Abel. “Even a slow, and relatively accessible oil spill like this one has clearly stretched New Zealand’s response capability to its limits.”

“It is also a potential disaster for the blue whales and dolphins presently calving in the area, as well as numerous other marine species,” he said.

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 they would make it a priority to remove those goods as part of their operation.