In this photo provided by Maritime New Zealand, shipping containers float Wednesday, …

TAURANGA, New Zealand (AP) — A cargo ship that has spilled hundreds of tons of oil since striking a reef off New Zealand's coast appeared to be breaking up in heavy seas, as its captain faced criminal charges in court Wednesday.

A vertical crack was apparent from the deck to the waterline of the Liberian-flagged Rena, which ran aground Oct. 5 on Astrolabe Reef, 14 miles (22 kilometers) from Tauranga Harbour on New Zealand's North Island. About 70 containers have fallen off the deck of the 775-foot (236-meter) vessel as it has listed increasingly in the worsening ocean conditions.

Maritime New Zealand, which is managing the emergency response, described the crack as a "substantial structural failure" and warned that the stern may break away. Three tug boats were mobilized to hold the stern on the reef while efforts are made to remove the oil from the ship, or to tow the stern to shallow water, the agency said in a statement.

Weather on the reef was terrible Wednesday, with swells up to 16 feet (5 meters), Maritime New Zealand spokesman Steve Jones told The Associated Press. The brutal conditions were making it impossible for a salvage crew to board the ship, he said. Without the salvage crew aboard, oil cannot be pumped out of the ship.

"It's appalling," Jones said of the weather. "Everything is still in a holding pattern."

Forecasters were predicting the swells would ease to 6 feet (2 meters) by Thursday, at which point salvage crews might be able to try to board the ship, Jones said.

The piles of containers that remain on deck have continued to move, making it dangerous for salvage crews to work on board. Six vessels have been mobilized to intercept the drifting containers and other debris in the water.

There were 1,368 containers on board, 11 of which contained hazardous substances, the maritime agency said. The containers with hazardous materials were not among the 70 that had fallen overboard, Jones said. Still, it is highly likely that more containers will topple off because of the rough weather and the ship's steep list, he said.

The 44-year-old Filipino captain, whose name has not been revealed publicly, was charged with operating a vessel in a manner causing unnecessary danger or risk and was released on bail Wednesday at Tauranga District Court. The ship's second officer is to face a similar charge on Thursday.

The captain's lawyer, Paul Mabey, requested that Judge Robert Wolff withhold his client's name because, he said, "there is a real potential that some persons may want to take matters into their own hands," the New Zealand Herald reported on its website. It also said the grounding occurred on the captain's birthday.

If convicted, the captain could face a fine of up to 10,000 New Zealand dollars ($7,800) and 12 months in prison. His next court appearance is Oct. 19, when authorities say more charges are likely.

Maritime New Zealand commander Nick Quinn said his priority remained cleaning up the oil.

"Until now, we have had a light oiling of beaches," he said. "This will significantly increase as more oil washes ashore over the coming days."

The government has demanded to know why the ship crashed into the well-charted reef in calm weather, but the vessel's owner has given no explanation.

Maritime New Zealand estimates that between 220 and 330 tons (200 and 300 metric tons) of heavy fuel oil have spilled from the hull, leading New Zealand's environment minister, Nick Smith, to call it the country's biggest maritime environmental disaster.

Officials believe the ship had about 1,870 tons (1,700 metric tons) of oil and 220 tons (200 metric tons) of diesel on board before it started leaking.

Clumps of oil have washed up on pristine beaches near Tauranga. Maritime New Zealand spokeswoman Anne Coughlan said 200 oiled birds had been found dead and 41 others were being cleaned at a wildlife emergency center.

Witnesses said dead fish were also washing ashore as local volunteers with plastic gloves and buckets worked to clean the oily clots from the white sand.

In a statement, the owners of the vessel, 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.

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