Salvors are installing sliding beams on the bow section of the Rena wreck at Astrolabe Reef to shift containers overboard so that they can be recovered.

The position of the wreck on the reef, in particular the sunken stern section, make it difficult for the Smit Borneo crane barge to get close enough to the bow to lift containers off it.

Divers stand on the top of the sunken accommodation section of the Rena with the Smit Borneo crane barge nearby. Photo: Maritime New Zealand.

By sliding the containers into the water, the Smit Borneo crane will be able to reach and recover the containers.

There are 340-400 containers on the bow section of the wreck.

In total there were 1369 containers onboard the Rena when it ran aground on the reef on October 5.

Maritime New Zealand estimates about half of these containers have been lifted off the wreck or have fallen off in storms.

MNZ says it is impossible to estimate the total number still inside the sunken stern section, but it is expected that most to have fallen from the vessel have sunken at or near the reef.

On Wednesday salvors removed one container from the wreck. It contained paper products.

The weather today is deteriorating at the wreck with wind rising to 20knots and swells increasing from 1m to 2m.

The rough weather is forecast to remain on Friday and settle on Saturday.

Container and debris recovery contractor Braemar Howells has unloaded the dangerous goods containers removed from the bow section.

These containers held empty hydrogen peroxide tanks and Maritime New Zealand reports they did not pose a major hazard.

An observation flight of the wreck this morning revealed a light silver and rainbow sheen is stretching south of the wreck for about 4km.