Container removal from Rena, the cargo ship grounded on the Astrolabe Reef, is set to get more difficult in the coming weeks.

Maritime New Zealand national on scene commander Rob Service says the container removal operation is becoming progressively more difficult.

Salvors secure lines for lifting containers off Rena. Photo: LOC

The difficulty is such operations will need to stop during periods of high winds and swells.

He says there has always been concern about how long the operation will take, but it has to be undertaken safely, with each stack of containers being individually managed.

Salvors have lifted 165 containers from the ship since it stranded on the reef on October 5 with 1368 containers aboard.

A storm on October 12 lashed the ship causing 88 to fall off.

Salvors removed 20 containers on Tuesday, November 29.

The ship remains intact and a light sheen of oil is visible extending from the vessel.

Low level beach cleaning is taking place at Mount Maunganui, Maketu, Matakana and Motiti Island today, and in Papamoa where oil has resurfaced.

Rob says oil deposited on the beaches is likely to be covered and uncovered by normal coastal processes for some time.

However, the amount of oil is not significant and overall the amount of oil is decreasing.

A wildlife response team also captured and examined 80 penguins on Rabbit Island last night but found no oiled birds.

Thirteen of these birds were previously oiled birds that had been cleaned and rehabilitated and returned to their natural habitats.

MNZ is planning the release of the remaining 240 little blue penguins at the Wildlife Centre in Te Maunga as soon as their habitats have been given the all clear.