Another 10 containers have fallen off the Rena as heavy swells batter the fragile wreck.
Maritime New Zealand has confirmed swells of up to 7m had forced a hatch cover off the number three hold in the bow section of the stricken ship, letting about 10 containers fall into the sea.
Bad weather two weeks ago had already dislodged a number of containers, wooden debris and oil, and response and recovery manager David Billington said today's loss was not unexpected.
The ship has been in a fragile state for some time.
Much of the stern was sitting beneath the water after the Rena snapped in half on January 9, three months after it struck the reef off the Tauranga coast in October last year.
Billington said one container was seen floating near the wreck, but it was possible the others had sunk to the seabed.
He said no salvage operations would take place during the rough weather, but the salvage and container recovery teams were monitoring the situation and had contingency plans in place to respond as soon as weather conditions allowed.
Maritime NZ National on scene commander Rob Service said the rough seas had caused further damage to the wreck and a small amount of oil had again seeped into the ocean.
"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," Service said.
Maritime NZ said there were about 649 containers now accounted for onshore, made up of 575 containers removed from the Rena, and about 74 retrieved from the sea and shoreline.
Heavy wind and rough seas on the Astrolabe reef are expected to carry on through tonight and ease tomorrow.