Up to 300 containers from the stricken ship Rena have been washed overboard and most are likely to sink, authorities say.

At a press conference held in Tauranga a spokeswoman from environmental cleanup specialist Braemar Howells Claudine Sharpe said "between 200 to 300 containers" had been washed overboard after the ship was pounded by heavy swells up to 6 metres on Saturday night.

The ship's stern is now listing at 23 degrees to starboard while the bow section remains firmly wedged on Astrolabe Reef, where it crashed into on October 5.

Earlier this morning Maritime New Zealand officials flew over the ship which was surrounded by murky waters as tonnes of milk powder from one of the ship's containers spilled out.


Of the missing containers, Ms Sharpe said 30 had been identified and 15 of those tagged and corralled in an offshore area.

"At this stage we have lost quite a lot of containers," she said.

"We are looking at a round figure of around 200 to 300 cotnainers. Of those 20 per cent will float - the remainder will sink."

Ms Sharpe said the top most containers had been tagged with transponders and she was confident these would be recovered.

She said resources were in place if anything comes ashore.

"We will deal with it but as I said our main priority is to stop it coming ashore if we can."

Maritime New Zealand salvage unit manager Dave Billington said reports of containers being lost overboard started coming through last night about 8pm.

He said MNZ staff viewed the ship this morning and found its after part had swung about 13 degrees to starboard and had completely seperated from the forepart.

"The distance we estimate is about 20 to 30 metres," he said.

"The ship has broken clean in two."

Fears are mounting further oil could leak.

Mr van Wijngaarden said it was very unlikely that oil reported ashore today was from last night's break-up of the Rena because wind and tides had initially taken it off-shore, and was thought to be old oil that had been remobilised due to the recent rough weather.

"Any oil coming ashore in the coming days is expected to be much less the amount that washed up after the Rena first went aground.

"Current modelling suggests that beaches south east of Mt Maunganui are most likely to be affected by oil and debris, which includes milk powder and timber. Anyone finding oil or debris is asked to report it immediately to 0800 645 774 and to stay well clear, as all debris must be treated as if it is contaminated.

National On Scene Commander Alex van Wijngaarden said no Tauranga beaches had been closed, but local surf life savers today advised people to stay out of the water because of the debris and sea conditions.

"We reiterate the message that people need to exercise their common sense and not swim or surf where there is likely to be containers, debris or oil coming ashore. Also we ask that people keep clear of any debris or oil, and report it to us so that our trained people can come and clean it up."

Wind and sea conditions were constantly being modelled to plot the trajectory of oil and debris. There is no way of knowing exactly how much oil was released from the duct keel when Rena's bow and stern separated, but some could still be trapped in the stern section.

Communities along the Bay of Plenty coastline are being advised that debris and oil is likely to start coming ashore tonight and tomorrow.

The vessel ran aground the reef on October 5, spilling hundreds of tonnes of oil and containers into the ocean which took months of clean-up efforts. Spilt oil killed hundreds of birds.

Just last week the ship was pounded by bad weather, causing it to break into two pieces which remained firmly on the reef.

The Bay of Plenty Regional Council has issued navigational warnings for shipping and boat users to avoid new hazards fallen from the ship.

Floating containers have been found northwest of the Rena. A large amount of debris has been sighted downwind of the vessel, and more is expected to wash ashore today.

The debris includes timber and bags of milk powder.

Bay of Plenty Regional Council water management group manager Eddie Grogan said the regional council was currently reassessing the three nautical mile exclusion zone around the Rena.

"We will provide more information once we've assessed the situation, however we anticipate the exclusion zone will be increased,"' he said.

He said while the conditions might be good for surfers, people should be aware that a large amount of debris is in the water including the area from Waihi Beach to Mayor Island to Maketu.

"We're asking people to be conscious of the hazards and to be sensible and careful."

The National Response Team has been activated to respond to the potential release of oil from the ship and treat any affected wildlife.

Weather conditions continued to be poor, with severe weather expected to pound the area for the next three to four days.

All vessels in the area are recommended to navigate with extreme caution.

Bay of Plenty Regional Council recommends all vessels to proceed at slow speed, keep a good lookout and travel through the area in daylight only. The debris field is extensive and its movement is unpredictable and could extend further.

They say anyone found in the exclusion zone without the express permission of the harbourmaster may be fined $200 or could be prosecuted.

Anyone sighting oil or containers in the water is asked to phone 0800 645 774.

- additional reporting APNZ