Large swells and wind caused further damage to the Rena on Saturday night.
Maritime New Zealand says the crack in the hull is open further, but ''she may still be connected underwater''.
The aft section of the ship is ''moving more freely'' than the forward part.
The agency says the extent of the damage will need to be verified by divers, but the vessel remains firmly grounded and there is no way it can be towed off the reef.
[image:4227:full]It was the fourth storm since the Rena went aground on the Astrolabe reef on 5 October.
At least two containers have washed overboard. Four vessels are searching for them.
A helicopter flight has confirmed more timber and packets of milk powder have washed ashore on Motiti Island
Shoreline surveys have also found more debris washed ashore.
Maritime New Zealand says the weather is expected to improve over the next few days but further damage is possible and barges are on standby.
But if the ship does break up, Maritime NZ says it has plans in place to tow it away.
