Salvors are hopeful to begin pumping oil off stricken container ship Rena tomorrow evening but say the job will not be complete before the forecast high winds and large swells descend on the Bay of Plenty.

Maritime New Zealand advisor Captain John Walker, who has flown in from Singapore, has 16 years experience salvaging ships around the world and said the complexity of the task ahead was "very high" due to the 11 degree list of the vessel and the fact the front of the ship was firmly grounded while the rear floated free.

The 20 person salvage team includes experts from the United Kingdom, Australia, Singapore and Holland.

"You've go the best salvage team I would say in the world," Mr Walker said.

Pumps and hoses will be flown by heavy lift helicopter onto the ship and the oil transferred onto the barge Awanuia.

"We are hopeful that we may start pumping tomorrow evening," he said.

Once the oil has been removed Mr Walker said the draft salvage plan required the removal of the containers on board in order to lighten the ship which continues to crush down on the reef.

Naval architects are currently on board Rena assessing the strength and stability of the vessel.

Svitzer have also chartered a 747 plane to bring equipment needed for the salvage from their Sydney warehouse. A second RNZAF plane is also being used to bring equipment to the region.

Meanwhile, more heavy fuel oil spilled from the ship this afternoon and Maritime New Zealand national on scene commander Rob Service said dispersant was being sprayed on this from a vessel.

The on-water recovery of oil got underway this afternoon however, Mr Service said dispersant remained the most effective method of fighting the spill.

The New Zealand Fire Service is also on hand at the Port of Tauranga to assist with the decontamination of on-water responders to the spill and vessels involved in the clean-up.