New Zealand’s worst maritime environmental disaster gets worse as ship splits in two, spilling cargo and debris.

The Rena separated into two after being battered by waves [Reuters]

A cargo ship grounded off the New Zealand coast since October has split in two, spilling sea containers and debris and sparking fears of a fresh oil spill, maritime officials said.

The wreck of the Greek-owned Rena was described as New Zealand’s worst maritime environmental disaster even before the rear section of the ship, lashed by pounding seas, broke away on Sunday.

The ship previously spilled heavy fuel oil that fouled pristine North Island beaches and killed up to 20,000 seabirds, and despite salvage efforts nearly 400 tonnes of oil remains onboard.

Maritime officials said the front section of the wreck remains stuck in its original position, but the stern section slipped at least 30 metres away from the bow and is “moving significantly,” pounded by 6-meter swells.

“We have had a significant release of containers… and a significant release of debris from those containers,” Maritime New Zealand spokesperson Ross Henderson told Al Jazeera.

“It doesn’t pose any health risk but if it does come ashore we are warning people to be weary that debris may come ashore.”

He warned that the storm that split the vessel 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 on Sunday.

Alex van Wijngaarden, on-scene commander for the national response team, said oil could come ashore around midnight on Sunday.

“While reports at this stage indicate there has not been a significant release of oil, with the Rena in its current fragile state, a further release is likely,” he said.

“While it is unknown at this stage exactly how much oil may be released, teams have been mobilised and will be ready to respond to anything that may come ashore.”

Stranded since October

The Rena ran aground on Astrolabe Reef 22km from Tauranga Harbour on North Island on October 5.

Salvage crews have removed more than 1,100 tonnes of oil from the stricken vessel but about 385 tonnes 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.

At least 23 containers were lost from the ship when it broke apart, and more were likely to be lost, said David Billington, a salvage unit manager for Maritime New Zealand.

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, but 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.

The Rena, like many ships, is registered in Liberia. Some 10 weeks later, the Rena ran full-steam into a well-marked reef off the coast of New Zealand.

It is not clear whether the previously identified problems played any role.

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.