Salvage workers in New Zealand said Monday they expect more oil to leak from a grounded container ship off the country's coast.

Spokesmen said crews managed to pump only about 20 tons of heavy fuel from the crippled ship overnight, leaving at least 1,300 tons of oil in the tanks. Around 300 tons has already leaked from the Liberian-flagged Rena, fouling kilometers of beaches in the Bay of Plenty and killing about 1,300 birds.

Bruce Anderson, who is heading the salvage operation, said the ship is close to breaking up and it is just a matter of time until more oil is released.

But the salvage chief said it is not clear what will happen when high seas finally crack open the badly damaged ship.

The ship's captain and second officer, who was navigating the ship when it 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.