The cargo ship Rena's precarious state will be put to the test this weekend by some of the worst severe weather since the vessel grounded in October.

Maritime New Zealand this morning said a low pressure system was forecast to arrive on Saturday afternoon, with the worst severe weather predicted for Sunday.

Swells of up to seven metres are expected to hit the Astrolabe Reef near Tauranga, where the ship has all but broken in two after being lashed by months of waves.

The weather is some of the worst to be forecast so far.


The Rena remains in a fragile but stable condition, with electronic sensors on board showing no significant change.

Divers have so far been unable to inspect the underside of the vessel to see whether the two parts of the vessel were still attached below the surface.

Containers on the bow of the vessel have been lashed down and those that are safely accessible have been fitted with location transponders ahead of the anticipated bad weather.

Salvors were constructing a temporary gangway between the forward and aft sections of the broken ship, ahead of a more permanent structure to be put in place.

They would today make the most of calmer conditions before the severe weather hits.

Cloudy periods and showers were expected today and tomorrow, with swells of about 1m at the reef today.

Salvors removed 14 containers yesterday from the no.7 hold, leaving an estimated 898 containers still on board Rena.

They would today focus on removing containers from the no.6 hold, which was easiest to access, and would pump gas from the no.5 hold to make it safe once that was completed.

Container clean-up contractors Braemar Howells this morning continued picking up container debris between Papamoa Beach and Maketu, while wood was reported at Motiti Island.

The debris was mainly plastic and milk powder, and some meat products.

The company has warned that some milk powder packets have opened after arriving on shore, and urged the public not to touch the material, as it was a potential health hazard.

Sonar vessel searches yesterday found six potential containers which would be inspected by camera.

Oil clean-up teams remain on standby in anticipation of further spills, and shoreline assessments will take place today.

A patch of oil with a metallic sheen, some 10-30m wide and 3km long, extends from the vessel towards the north.