Maritime authorities believe up to 300 containers may have been lost from the battered Rena when it split off the Tauranga coast overnight.



The ship finally relented in 7-metre seas and has broken in two, but remains wedged on the Astrolabe reef where it has sat since October 5.



At a press conference this afternoon Environment Minister Nick Smith played down the size of the problem, despite an unknown quantity of oil seen leaching from the broken ship.



''The risks for the environment are a fraction of what they were in October,'' said Smith.

Salvors had already removed more than 1000 tonnes of oil from the ship but some remains onboard.

Of the 837 containers on board the Rena yesterday, authorities believe that between 200 and 300 had now washed overboard.



Of those, between 20 and 30 per cent had been fitted with monitoring devices. Around 30 containers had already been found.

FRESH SAFETY WARNINGS

MNZ salvage unit manager David Billington said the Rena's forward section was firmly wedged on the reef, but the aft had separated and moved to starboard about 13 degrees. There was a 30-metre gap between the two pieces.



Billington said the fresh damage had resulted in a large number of containers and debris being thrown into the sea.



"While the two sections of the Rena currently remain on the reef, there's no question the ship is badly damaged with the severe movement breaking off many of the hatch covers and releasing containers from the holds,'' Billington said.



"Salvors are now working to assess the state of the vessel so that naval architects can undertake further calculations to gain a clearer picture of its ongoing stability."

Billington said more containers were likely to be lost. There was also a large debris trail, including wood, around the vessel. The tug Go Canopus was connected to the aft section of the Rena and was continuing to monitor its status.



Container recovery company Braemar Howells had tugs en route to tag containers with buoys as it was too rough to tow or recover them, while vessels with trawl nets would be sent to collect debris once weather conditions improved.

MNZ's national on scene commander, Alex van Wijngaarden, said the National Response Team had been mobilised, which included trained oil spill response and wildlife experts, to prepare for more oil coming ashore.



"While reports at this stage indicate there has not been a significant release of oil, with the Rena in its current fragile state, a further release is likely," Wijngaarden said.



"At this stage, preliminary trajectory modelling predicts that any oil released will come ashore around midnight tonight, landing on beaches south east of Mt Maunganui. However, this could change at any time depending on the weather and wind conditions.''

The Bay of Plenty Regional Council said it had issued fresh navigation warnings because of the debris from the ship.



Floating containers had been seen to the northwest of the Rena and a large amount of debris had also been sighted downwind.

EXCLUSION ZONE LIKELY TO BE EXTENDED

Regional Council water management group manager Eddie Grogan said it was re-assessing the maritime 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," Grogan said.



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



"Personal safety is our top priority, so we're asking people to not put themselves in situations where they could get injured."



It was important to notify MNZ if people discovered oil or containers in the water. They could call 0800 645 774, he said.

Mark Tucker, director of Tauranga-based Bay Dolphin Swims, said the weather was ''very nasty'' and most boats wouldn't be going out until Tuesday at the earliest.



''Last night it was a real storm, but it's abating a bit now,'' Tucker said.



''There's a south-easterly wind blowing at about 20 knots.



''The sea is very sharp and short, not comfortable at all.''



Tucker, who had recently started site-seeing tours to the Rena, anticipated the boat exclusion zone may be extended from 3 to 10 nautical miles.



''[The mess] will be huge. Maybe not so much the oil, but containers and debris.''



Tucker said the south-east wind meant any new oil spill would likely be blown out to sea but other cargo, including meat, timber, deer hides and 400kg bales of recyclable plastics, could pose a danger to boats.



''It's not good the oil is going out to sea but at least it won't be on the beaches.''



Tucker understood the next move would be to tow the back half of Rena back to shore where it could be dismantled and removed.



''At the end of the day they can't leave anything behind.''

The Rena's captain and the navigation officer have been charged over the ship's grounding, and are due to reappear in court on February 29.