New Zealand shipping authorities said Thursday they had filed pollution-related charges against the owners of Liberian-flagged cargo ship that grounded on a reef off the east of New Zealand's North Island six months ago.

Maritime New Zealand (MNZ) said Greece-based Daina Shipping Co. had been charged under New Zealand's Resource Management Act 1991 in connection with the "discharge of harmful substances from ships " in the coastal marine area.

The charge carried a maximum fine of 600,000 NZ dollars (489, 356 U.S. dollars) and 10,000 NZ dollars for every day the offending continued, said a statement from MNZ.

Daina Shipping Co., a subsidiary of Greece's Costamare Inc., was the registered owner of Rena, and had overall responsibility for the operation of the ship, which grounded on the Astrolabe Reef on Oct. 5 last year.

The charge had been filed in the Tauranga District Court and was expected to have its first call on May 25.

The prosecution followed the Feb. 29 guilty pleas by the Rena's master and second officer to charges laid by MNZ last year.

The identities of the two men were suppressed when they appeared at the Tauranga District Court.

The captain pleaded guilty to operating a vessel in a manner causing unnecessary danger or risk, discharge of harmful substances from ships or offshore installations, and four charges of wilfully attempting to pervert the course of justice by altering ships documents.

The second officer admitted operating a vessel in a manner causing unnecessary danger or risk and three charges of wilfully attempting to pervert the course of justice by altering ships documents, but entered no plea on a charge of discharge of harmful substances from ships or offshore installations.

Sentencing of both men was set for May 25 at the Tauranga District Court.

The statement said MNZ would lay no further charges in relation to the grounding, and would make no further comment while the matter was before the courts.

The Rena spilled hundreds of tonnes of oil into the sea along with cargo containers and their contents, killing an unknown number of New Zealand's native birds and prompted a massive clean-up of oil from beaches around Tauranga.

On Jan. 7, the vessel split in two and salvors are still trying to remove cargo containers from it.

The rear half of the ship finally sank on Wednesday after being battered by rough seas.