Maritime New Zealand is reporting the overnight storm washed two containers overboard from the Rena and parted lines securing the barge Smit Borneo to the wreck.

The 236m container ship itself remains hard aground on the Astrolabe Reef.

Rena, just before the storm started on December 14. Photo: LOC.

One of the containers washed overboard has sunk with its cargo of aluminium chairs.

The other, containing a cargo of timber, remains afloat. It is fitted with a transponder and when located will be towed and lifted onboard the barge Sea Tow 60.

The search for the sunken container, which is inside the exclusion zone, will continue.

Sensors onboard the Rena detected some additional movement during the storm, but there is no overall change to the status of the vessel. It remains in a fragile state, but aground.

Lines connecting the Smit Borneo to the Rena parted overnight in the rough weather.

The barge experienced rolling of 5-6 degrees.

The weather peaked at about 10pm with a combined sea state of 6m.

A damaged cable on Smit Borneo's crane has been replaced, but container lifting operations continue to be hampered by bad weather.

This morning's reconnaissance flight over the Rena noted two distinct narrow tracks of rainbow sheen about 30-50m wide stretching 1-2km from the ship.

The sea swell is dying away today and winds from the northeast are turning northwesterly this morning.

The patchy weather is set to continue over the next couple of days with northeasterly winds of up to 40 knots, 74km/h, expected to peak late Saturday.

Fine weather is forecast for Sunday.