Oil and shipping containers are spilling from the Rena as heavy swells of up to 7m batter the wrecked ship.

Maritime New Zealand today confirmed the rough seas had caused further damage to the cargo vessel, which ran aground last October before breaking apart in bad weather.

National on-scene commander Rob Service said a small amount of oil had been observed in the immediate vicinity of the wreck.

"There is only a small amount of oil remaining on the wreck but, as we saw last week, even a small release can result in patches of oil reaching the shoreline," he said.


Trajectory modelling shows the oil could reach the Coromandel shoreline overnight. That could result in a light sprinkling of oil between Whiritoa and Whitianga.

The total amount of oil left on the Rena was in the tens of tonnes - far less than the amount released during the big spill in October - and it was very unlikely it would all be released in one event.

The rough seas have also forced open a hatch on the bow section, releasing an estimated 10 containers from the hold.

Maritime New Zealand response and recovery Manager David Billington said one container was seen floating near the wreck.

The others had possibly sunk to the seabed.

Mr Billington said no salvage operations could take place during the rough weather.

Salvage and container recovery teams were monitoring the situation and had contingency plans in place to respond as soon as the weather allowed.

He warned Bay of Plenty to heed the two nautical mile exclusion zone around the wreck and to look out for debris.

"There is debris in the water and this could cause damage if it comes into contact with your boat. Keep a really good lookout, and travel at a safe speed."

The heavy seas of up to 7m are forecast to persist through the night, and ease tomorrow.

WeatherWatch head weather analyst Philip Duncan said the biggest swells from a tropical storm north of New Zealand would arrive in the Bay of Plenty tonight and early tomorrow morning.

Mr Duncan advised people to stay out of the sea for Wednesday and Thursday as big swells, gales and rain moved in.