The master salvor working on the bow section of the Rena says the salvage and wreck removal of the container ship is one of the most expensive in the world.
The ship ran aground on the Astrolabe reef, off Tauranga, on 5 October last year, causing New Zealand's worst maritime environmental disaster.
American-based company Resolve is working on the bow, cutting it into sections one metre below the waterline.
Master salvor Frank Leckey says it would not be impossible to remove the stern section from the reef, but it will be even more challenging than the bow.
The salvage and wreck removal is comparable to the capsizing of Italian cruise ship Costa Concordia in January as one of the most expensive, he says.
Mr Leckey has worked around the world and says the Rena has been one of his most difficult jobs because of the way the ship is sitting on the reef.
He says the next few months will be extremely difficult and dangerous for his dive teams due to sea conditions and depth they will be working at. However, he is confident that work on the bow section will be finished by the end of this year.
Maritime New Zealand director Keith Manch estimates that removal of the wreck could take between 12 and 18 months.