Salvors on the stranded ship Rena are still at least three days away from gaining access to oil in a submerged fuel tank.
Nearly 900 tonnes of oil has been pumped off the ship, leaving about 600 tonnes still on board.
The Rena has been grounded on the Astrolabe reef 12 nautical miles off the coast of Tauranga since 5 October.
Maritime New Zealand's salvage unit manager, Kenny Crawford, says getting to the submerged starboard fuel tank is a complicated and dangerous task, and work on draining it might not be able to start until at least Monday.
The tank, which contains about 360 tonnes of oil, has to be accessed through several hatchways and levels.
Beaches still best cleaned manually
Meanwhile, Maritime New Zealand says the five to eight tonnes of oil that spilt last weekend has remained within an 8km radius of the ship.
It says machinery that can be used to sift through sand for washed-up oil is being tested, but so far the best method of cleaning the beaches is by hand.
Just over 800 tonnes of oily waste has been removed from Bay of Plenty beaches so far.