Further oil and containers are expected to start washing up on Bay of Plenty beaches overnight as the storm that tore the Rena into two pieces also sent up to 300 containers overboard.

Maritime New Zealand estimates between 200 and 300 containers were lost overboard when swells of up to 7m bashed the ship in the early hours of Sunday morning.

Of these 20 per cent of the containers are tagged and can be tracked, and 15 have been corralled into anchorage points, ready to be brought to shore when weather permits.

Claudine Sharp, from Braemar Howells, the company responsible for processing of containers, says at last count 837 containers remained on board the Rena and approximately 550 containers remain on the wreck.

'At the moment the sea state is very severe, so we are working on locating and corralling all of the containers we can to the various anchor points.”

It is believed 21 containers carrying the hazardous substance cryolite are included in the 200 to 300 containers lost during the night and these are thought to have sunk to the bottom of the ocean. They are deemed to be little environmental risk.

'We know they were located in the hatches where containers have been lost. They are very heavy so it is likely they have sunk.”

Claudine says in the current weather conditions the containers are expected to head west past Matakana Island, but with a change in the weather expected overnight this could change.

Residents at Harrisons Cut have also been given 24 hour's notice, should the area need to be used for container processing operations.

'We have looked at activating Harrison's Cut as a processing site. However this is just a contingency and is not our main plan.”

MNZ salvage unit manager David Billington says the ship's position started to change at 8pm on Saturday, January 7 with reports of containers lost overboard.

'At first light this morning we were able to view the weather camera and we saw how the vessel had changed.”

David says the stern part of the ship has now completely detached from the bow of the ship, and is listing 24 degrees starboard.

MNZ salvage advisor Jon Walker says the bow of the ship is firmly grounded on the reef and will slowly deteriorate over time.

'It is not likely the bow section of the ship will move off the reef.”

He says if the stern of the ship were to move off the reef there is the possibility it could be towed to shallow waters, however it would depend on the weather.

'If the stern of the ship were to float we could tow it place where it will be easily accessible to remove containers.”

He says with the stern of the ship still moving on the reef there is a possibility it will sink.

MNZ National On Scene Commander Alex van Wijngaarden says patches of dark oil can be seen amongst a sheen of silver oil coming from the wreck.

He says in the current weather conditions the trajectory for the oil will hit the beaches from Mount Maunganui east towards Omanu and Papamoa and is expected to arrive on beaches by midday tomorrow.

'At the moment the trajectory shows the free flowing oil will head eastwards from the Mount. However this is just a trajectory and it could change.”

Environment Minister Nick Smith says the change in the vessel's condition is 'serious but not unexpected”.

'We were told by Maritime New Zealand when the ship first grounded that swells of up to 6m could break the ship apart.”

Nick says the risks are only a fraction of what they were when the ship first grounded on October 5, carrying more than 1700 tonnes of heavy fuel oil.

More than 1000 tonnes of heavy fuel oil has been pumped from the ship, while it is estimated 350 tonnes leaked from the ship during a storm on October 11.

He says it is unlikely the beaches will close this time, due to the small amount of oil expected to wash up.

'It is likely to be tens of tonnes, not hundreds of tonnes.”

A National Response Team has been activated and Alex says teams are arriving in Tauranga tonight to respond to the change in situation.

This includes Defence Force personnel who will help to assist in the clearance of shipping channels and in enforcement of the three nautical mile exclusion zone around the Astrolabe Reef.

Wildlife teams are also on standby and will be working around the Mount Maunganui and Motiti Island areas tonight searching for any oiled wildlife.

Anyone wanting to report containers or oil on beaches should contact 0800 645 774.

Seen containers, debris or oiled wildlife wash ashore? Phone 0800 SUNLIVE with your news tip. email photos to newsroom@thesun.co.nz