Heavy fuel oil remains in just one of Rena's fuel tanks – starboard five tank.

It is submerged and the hardest of the fuel tanks for salvors to extract oil from.

Working conditions aboard Rena for the salvors are murky. Photo: Maritime New Zealand.

In order to pump oil out of it, divers have for the last two weeks worked on modifying the inside of the ship stranded on the Astrolabe Reef since October 5.

This work has included the construction of a coffer dam to seal off the passageway above the tank from which the salvors will pump the 358 tonnes of oil found inside it.

They have pumped more than 1000 tonnes of heavy fuel oil so far from more than five different tanks.

Maritime New Zealand salvage unit manager Kenny Crawford says salvors are now removing some lighter oils too.

'While removing the remaining 358 tonnes of heavy fuel oil from the starboard tank remains the salvage team's highest priority, they are also taking the opportunity to remove hydraulic fluid and other lighter oils from other tanks in the ship that are easier to access.”