The cargo vessel ran aground on the Astrolabe Reef off the coast of Tauranga on October 5.
Containers transferred to the Port of Tauranga were being processed by container recovery company Braemar Howells.
Oil was still being skimmed from the starboard number 5 fuel oil tank and warm water washing was done at Mount Maunganui today to remove residual oil from the rocks.
"Following the good results we have seen from this, we will be doing more of this work over the next few days,'' said MNZ national on scene commander Alex van Wijngaarden.
Meanwhile, the first of the cleaned penguins affected by oil from the Rena are due to be released from the oiled wildlife facility tomorrow.
About 60 little blue penguins will be freed back into the wild from Mount Maunganui beach at 10am with possibly more released later this week.
More than 350 tonnes of oil spilled into the sea, killing hundreds of birds and than 400 affected birds have been taken into captivity for treatment.
All of the birds had to undergo blood tests and veterinarian checks to ensure they are ready for release, said national oiled wildlife response team co-ordinator Kerri Morgan.
They also had to pass a "six-hour test" where they swim for six hours without a break for assessment to ensure their waterproofing was returned.
"The oil coats the birds' feathers, which are designed to act as a waterproof coat. After the birds are washed, they preen themselves and that helps the feathers regain their waterproofing,''said Miss Morgan
It was important as much oil as possible was removed from the birds' habitats before they are released, and along with oil spill response teams, staff have been checking their habitats are ready, said Miss Morgan.
The cleaned, micro-chipped birds have been swimming in fresh water, but salt was introduced into their pools over several days to prepare them for swimming in the sea again.
Salvors have successfully pumped 1350 tonnes of oil off the ship, with only residual oil still to be removed.
Miss Morgan said although there was a risk of a further spill of the residual oil on board Rena, this risk had to be balanced against the risk of keeping the birds in captivity for too long.
"These are wild animals and they belong in the wild.
"We can't keep wild birds in captivity for an indefinite period of time without running the risk of disease or injury.''
Some birds need to finish waterproofing, so the release programme will continue for some time.
The wildlife facility at Te Maunga would be slowly dismantled as the cleaned birds moved through the washing, re-waterproofing and salt water process and became ready for release.
"A few permanent structures would remain until Rena is off the reef and there is no longer any risk of an oil spill from the wreck,'' Miss Morgan said.
