New Zealand forecasters said water swells in the Bay of Plenty are expected to be as high as five metres Tuesday, turning for worse the condition of the ill-fated cargo vessel MV Rena, which has already been struggling with swells up to three metres. Fears of ship breakup or another major oil spill are rising again.

MetService says the bad conditions could last until Wednesday, when wind directions change.

So far, salvage teams have been able to offload more than 1,000 tonnes of oil from the ship, but they have to cease operations for now due to the bad weather. About 358 tonnes of oil remain in the submerged starboard tank No. 5.

Maritime New Zealand salvage unit manager Kenny Crawford said salvagers had sealed up the areas they had been working in as a precaution against the rough weather.

"This should help limit further release of oil in the worst-case scenario of the ship breaking up."

So far, there was no reported change to the status of the Rena overnight, the Herald reported.

"I think the Bay of Plenty region should prepare for some oil to appear on the beaches in the next few days," Associate Transport Minister Nathan Guy said Monday.

"Of course this may not happen, but we are prepared for a considerable bout of bad weather."

MV Rena, a largo cargo vessel, has spilled more than 300 tonnes of oil into the sea after its hull was pierced in stormy seas on Oct. 11. Rena's situation is the worst environmental disaster of New Zealand yet.