Big cracks are showing on a stricken cargo ship, increasing the chances it will break up and spew more oil into the sea off Tauranga.
The Prime Minister and Maritime New Zealand on Wednesday confirmed that the hull of the 236-metre long Rena has ruptured.
The ship has been wedged on Astrolabe Reef since 5 October and an estimated 350 tonnes of toxic oil has spilled so far, washing up on Bay of Plenty beaches and killing birdlife. It continues to list heavily to starboard and about 70 containers have fallen into the sea.
The 47,000-tonne vessel is owned by Greek company Costamare and was heading towards Tauranga from Napier when it ran aground carrying 1700 tonnes of fuel more that 1300 containers, including 11 with dangerous goods.
Maritime New Zealand's salvage adviser Captain John Walker says there are cracks on both sides of the Rena and at least one is visibly getting worse.
Prime Minister John Key visited the Bay of Plenty on Wednesday and says it is clear there are substantial cracks and stress fractures in the hull, increasing the likelihood that its back half will break off.
Mr Key told Radio New Zealand's Checkpoint programme the front of the ship is stuck on a reef while the back is moving up and down with ocean swells, putting stress on the vessel.
He defended the Government's handling of the disaster, saying in comparison with similar incidents overseas its response has been swift, and those responsible for the disaster will be held to account. Insurance cover for the ship is capped and the rest of the salvage and clean-up costs will have to be borne by the Government, he says.
The ship's captain and navagational officer are facing charges under the Maritime Transport Act.
Tugs sent to stabilise ship
Three tugs have been mobilised to support the stern of the Rena. Maritime New Zealand says they will hold the stern on the reef until efforts can resume to remove oil from the vessel. It says if the ship breaks up, the tugs will tow the stern to shallow water where the oil can be removed.
Maritime New Zealand's national on-scene commander Nick Quinn says containers still on the vessel are continuing to move, making it extremely dangerous for salvage crews to work. Six vessels have been mobilised to intercept containers and other debris which has tumbled into the water.
Hundreds of people are now involved in land, sea and air operations to deal with the disaster. Mr Quinn warns that oil seen across beaches in the region is a light oiling, with significantly more oil expected ashore over coming days.
The area of the exclusion zone around the Rena has been extensively widened to cover about a quarter of the Bay of Plenty coastline. It stretches approximately 45km from Mount Maunganui to Matata, and about 40km out to sea as far as Mayor Island. Anyone found breaching it could be fined up to $20,000.
70 containers overboard
Maritime New Zealand says about 70 containers - none containing hazardous substances and most thought to be empty - have been lost from the back of the ship's starboard side and some containers on the port side are unstable.
The authority says the salvors are sending vessels to try to gather some of the containers together and a heavy lift crane is due to arrive on Thursday to recover them.
Police are warning people against trying to open any containers as they would be breaking the law.
A scientist for the National Institute of Water and Atmospheric Research says the biggest tides of the year will occur at the end of October offering the best chance to refloat the Rena.
Dr Rob Bell says the king tides will give extra leverage, but whether the ship will survive another two weeks on the reef is unknown.