Transport Minister Steven Joyce says the cost of setting up the response to the grounding of the container ship Rena has reached $14 million.
Mr Joyce told a news conference in Tauranga on Thursday afternoon that figure is expected to grow.
A week ago, he said the cost of the spill and cleanup was approaching $10 million.
The Rena has been grounded on Astrolabe reef for four weeks.
Mr Joyce says almost all of the $14 million figure is made up of costs incurred by Maritime New Zealand, the main Government agency involved in the oil spill response.
Buckling onboard causing problems
Maritime New Zealand says buckling on the Rena has made accessing a submerged fuel tank more difficult for the salvage team.
Salvors are setting up a second system to pump oil out of the tank on the vessel's starboard side that is holding about 360 tonnes of fuel.
Maritime New Zealand spokesperson Bruce Anderson, says buckling and a fracture, around where the ship hangs over deeper water, are complicating efforts to access the submerged tank.
He says divers will use a process called hot tapping to extract oil from the tank while it is still under water.
Mr Anderson says at the same time work will continue on blocking off the submerged passageway so it can be drained of water.