WELLINGTON (AP) ― A cargo ship grounded off the New Zealand coast since October has split into two pieces after being lashed by pounding seas, spilling sea containers and debris and sparking fears a fresh oil spill could wash ashore, maritime officials said Sunday.

The officials said that the front section of the wreck remains stuck in its original position, but the stern section has broken off, slipped at least 30 meters away from the bow and is “moving significantly,” pounded by six meter swells.

“There has been a significant discharge of containers and container debris from the ship,” said Maritime New Zealand spokesman Ross Henderson, warning that the storm will continue for another three to four days. The debris included timber, bags of milk powder and floating containers, all of which could begin washing ashore later Sunday.

Oil clean up teams had “been activated to respond to the potential release of oil from the ship and to treat any affected wildlife,” he said in a statement.

The Greek-owned Rena ran aground on Astrolabe Reef 22 kilometers from Tauranga Harbor on North Island on Oct. 5, spewing heavy fuel oil into the seas, fouling pristine beaches and killing up to 20,000 sea birds in what has been described as New Zealand’s worst maritime environmental disaster.

Salvage crews have removed more than 1,100 tons of oil from the stricken vessel. But about 385 tons remain on board ― about the same amount that has already leaked into the sea.

The crews have plucked 389 of the ship’s 1,370 loaded cargo containers from its decks since it ran aground, while some 98 have been washed over board in the past three months.

One eyewitness, Warwick Roberts, said the rear section was sliding along the reef.

The “stern has reared up and center section is not visible. Large breaking waves observed on bow,” he told the New Zealand Herald website.

A three-kilometer no-go zone is in force around the wreck.

Investigations by the Associated Press last month revealed that Australian authorities impounded the vessel, which like many ships is registered in Liberia, but then released it the next day after Liberian maritime authorities intervened, essentially saying the ship was safe to sail and the problems could be fixed later.

Some 10 weeks later, the Rena ran full-steam into a well-marked reef off the coast of New Zealand. The reef has been identified on charts for almost 200 years.

The captain and Rena’s navigating officer face criminal charges of operating a ship in a dangerous or risky manner, polluting the environment and altering the ship’s documents after the crash.