Maritime New Zealand says the transferring of 1300 tonnes of fuel oil from a stricken container ship off Tauranga could start on Saturday.
The Rena, owned by Greek company Costamare Shipping, was heading towards Tauranga from Napier when it ran aground on 5 October carrying 1700 tonnes of fuel and more than 1300 containers.
As much as 350 tonnes of oil has spilled and 88 containers have fallen overboard, affecting shipping lanes.
Fourteen containers have been recovered, but not one containing the dangerous chemical alkyl suphonic acid. Another 21 have been identified, but Maritime New Zealand warns members of the public not to open any that have washed up on beaches.
Salvage experts were back on the wrecked ship on Friday to begin what has been described as an extremely dangerous operation to get the remaining oil off the vessel. Two teams of three experts were flown out to the listing ship which was being buffeted by two- to three-metre swells.
Four platforms have been transported by helicopter to the ship to provide flat working surfaces for salvage crews. Maritime New Zealand salvage unit manager Bruce Anderson says once these are in place, teams working below deck will be able to start connecting the necessary equipment to pump the oil off the vessel.
Workers will try to get access to the oil in the ship's fuel tanks by opening a hatchway, or, if that does not work, by cutting into the hull. It is likely to take days to transfer the thick cold oil onto the Awanuia barge.
Matt Watson, a spokesperson for the company charged with the salvage operation, Svitzer, told Radio New Zealand's Morning Report programme conditions on the ship are extremely dangerous with oil-stained, slippery decks and pitch black conditions below decks. The ship was listing at 22 degrees to starboard on Friday.
Maritime New Zealand has urged news organisations not to put aircraft into a no-fly zone three nautical miles around the container ship grounded off the coast of Tauranga.
Flight showed ship appeared stable
Maritime New Zealand completed an observation flight over the Rena on Friday morning and said it seemed to be stable.
Mr Anderson said cracks in the hull did not appear to have moved much, which suggested the vessel was starting to rest of the reef.
Svitzer spokesperson Matt Watson says a plan is in place should part of the Rena sink. He says while the hull is well-placed on the reef, the back section is floating above 60 metres of deep sea.
"If the back section was to come off, there are two general approaches that could be taken.
"The tugs that are out there now could try and shunt that rear section if it comes off onto the reef as well. Another option could be to simply tow it into shallower water."
Port operations that were suspended overnight as containers and debris were entering shipping channels resumed at 6am on Friday. Aerial and sonar surveys were continuing, to make sure shipping lanes are kept free of hazards.
Meanwhile, the Navy is bringing in an extra boat, HMNZS Pukaki, to patrol the waters around the ship over the weekend to ensure recreational boaties stay well away.