The Rena is set to be battered this weekend by some of the largest sea swells to hit the cargo ship since it grounded on the Astrolabe Reef on October 5.

However officials are confident they have plans to deal with the worst-case scenario of the ship breaking up, 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 7.5 metres high are possible at 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.

Although the vessel is effectively in two parts, Maritime New Zealand said the forward and aft sections of the Rena remain firmly grounded on the reef.


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."

With the bad weather on the way, salvors will endeavour to remove as many containers from the vessel as possible today before bringing the crane barge Smit Borneo back to port.

Another 17 containers were removed from the vessel yesterday, leaving an estimated 881 containers left on the vessel.

Maritime New Zealand said work in the no.5 hold was stopped yesterday after high gas levels were detected. Breathing apparatus are on the vessel and the gas levels will continue to be monitored today.

Spitzer Salvage spokesperson Brian Dale told Radio New Zealand this morning he was not nervous about the upcoming wild weather.

"Ourselves and Maritime New Zealand have contingency plans in hand if the ship does start to break up.

"If it breaks up ... you endeavour to connect to [the Rena] and then stabilise it and stabilise it and hold it.

"If it sinks it sinks. Then it is a clean up operation.

"We are not going that far ... we take it minute by minute. We just plan for the worst and hope for the best."

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.

- Additional reporting: APNZ