Spilled fuel oil dirties the sand of Papamoa Beach, New Zealand, as heavy breakers roll ashore on Oct. 12, 2011. (AP Photo/Natacha Pisarenko)

Heavy seas off northern New Zealand have worsened a developing environment disaster following the grounding of a container ship.

On Wednesday, major cracks were seen in the side of the ship during overflights, according to multiple reports, leading to fears that the ship would break apart.

Oil spilled from the ship has continued to wash ashore, coating beaches in a sticky black mass, as seen on numerous images posted on line. Reports earlier this week estimated the amount of heavy fuel oil spilled into the hundreds of tons.

Meanwhile, cargo containers have begun to fall from the deck of the grounded MV Rena, after the pounding of 10- to 15-foot seas and 30-knot winds caused the stricken ship to list seriously.

Soldiers have been called out to clean up beaches, according to the New Zealand Herald. Residents were warned away from the oiled beaches, owing to the toxic nature of the oil. Face masks may need to be given to area residents, the Herald said on Wednesday.

The number of dead birds recovered has risen into the hundreds, and the number of birds killed is expected to rise further.

Weather data accessed by AccuWeather.com show a marked lessening of winds off northern North Island, the site of the shipwreck, as of late Wednesday, local time. High swells were beginning to lower.

Winds and seas will be increasingly favorable for salvage and cleanup work Thursday and Friday, AccuWeather.com meteorologists believe. Calmest winds and seas are forecast for Saturday and Sunday.