Salvagers went back aboard a grounded ship off New Zealand’s northeast coast Thursday in an urgent effort to drain its fuel tanks before the ship breaks in two.

Improved weather after days of fierce winds and high seas enabled the salvagers to re-board the Rena, which has developed huge cracks in its hull since it ran up on a reef more than a week ago.

About 300 tons of heavy fuel have already leaked, fouling beaches in what authorities are calling New Zealand’s worst environmental disaster. Salvage director Bruce Anderson says the damage to the ship will make it even harder to remove up to 1,400 tons of remaining fuel before the ship breaks in two.

The vessel is listing at about 20 degrees, causing 88 of its shipping containers to slide into the sea, where they have begun to break up. Thousands of spoiled hamburger patties have washed onto a nearby beach.

On-scene commander Nick Quinn says that is complicating the efforts of work crews who are trying to clear the fuel oil from the beaches before it spreads.

The ship’s captain and second officer, who was in charge of navigation when the ship ran up on a well-marked reef, both have been charged in court with operating a vessel in a manner causing unnecessary danger.

The Greek shipping company that owns the Rena issued a video statement Thursday apologizing to all those affected by the accident.