Salvors onboard the container ship Rena were forced to temporarily stop pumping seawater into a submerged fuel tank on Sunday because of escaping gases.
The 47,000 tonne container ship has been grounded off the coast of Tauranga since 5 October.
About 750 tonnes of seawater is being pumped into the starboard tank to bring heavy fuel oil to the top so it can be pumped to a bunker barge.
Maritime New Zealand's salvage unit manager Kenny Crawford says as water filled the tank, gases escaped into the alleyway that runs across the ship.
He says the gases had to be vented before salvors could re-enter the corridor leading to the submerged tank.
Mr Crawford says it took four to five hours and then pumping seawater into the tank resumed.
He says more than 20 salvors worked on board the Rena on Sunday, with teams pumping 22 tonnes of lubricating oil out of Rena's engine room onto a barge.
Mr Crawford says that work progressed alongside preparations to extract the remaining 358 tonnes of heavy fuel oil from the vessel's submerged starboard wing tank.
Maritime New Zealand says sonar searches for sunken containers from the Rena have continued and a large number have been found.
Underwater transponders have been fixed to four containers known to contain hazardous goods, so they can be easily located should they be lost overboard.
Assistant National On Scene Commander Andrew Berry said sonar scans of the seabed have continued, to try and locate more of the containers.
Several have been located on the seabed within 1km of the vessel.
The container barge ST60 will begin trials in the Bay of Plenty this week but efforts to lift containers off the Rena will not begin until after the last of the oil has been removed.