Ferocious weather could make it too dangerous for salvors to approach the Rena if it breaks up in rough seas predicted for the weekend.
But officials say they have plans to deal with the worst, and crews on the shore would have at least 12 hours to prepare before oil or debris reached Bay of Plenty beaches.
Swells up to several metres high are expected to hit the Astrolabe Reef near Tauranga, where the ship has all but broken in two after being lashed by waves since it ran aground in October.
A low pressure system near New Caledonia is predicted to shift southeast on Saturday, bringing winds up 50km/h to the area around the Rena.
MetService weather ambassador Bob McDavitt said 3m to 4m-high waves could hit the ship several times an hour, but the highest 7.5m waves would be a once-a-day occurrence.
The Rena had survived winds of similar strength in the last week of December, and the worst of the weather would be centred further to the east at Gisborne, he said.
"The Rena has seen stronger winds and waves ... but the Rena is also in a state of decay.''
Divers have been unable to see if the two parts of the vessel are still connected below the surface.
Containers on the bow have been lashed down and the more accessible have been fitted with location transponders.
Salvage unit manager Kenny Crawford said the split in the broken vessel had become too wide for salvors to step over it so they were constructing a temporary gangway between the two sections before a more permanent structure was built.
In the event of a break-up, salvors would decide on action depending on the conditions.
"If it breaks in half in seven-metre waves, are you going to put people in the way of danger? It's an assessment we'll make at that time.''
National on-scene commander Alex van Wijngaarden said shore response crews would also have to "wait and see. Our plans are in place and we're ready to mobilise at short notice''.
The national oiled wildlife centre at Mt Maunganui had been downgraded, but it could be quickly brought back into action.
- Jamie Morton of the NZ Herald/additional reporting APNZ
