Some containers on the grounded container ship Rena are so damaged they are breaking up as a crane tries to remove them.
Maritime New Zealand says further salvage work will slow as a result.
Spokesperson Sophie Hazelhurst says it is hard to estimate how many containers will be able to be moved each day, but it will be a lot slower than the peak of 10 per day.
"They've been crushed by the movement of the ship and the containers that have fallen on top of them. So they're in a very weakened state.
''When the crane tries to pick them up they break up as they're lifted off so we then need to remove the rest of the container piece by piece," said Ms Hazlehurst.
She says most of the containers that have been lifted off have been empty but refrigerated containers are being hauled off now and have decomposed food inside.
A further six containers were removed on Sunday from the grounded container ship but the work is expected to slow.
A total of 46 containers have now been taken from the Rena, with 40 brought to shore.
The ship ran aground off the coast of Tauranga on 5 October and almost 1300 containers still need to be removed.
Meanwhile, oil washed ashore at Papamoa beach on Sunday and was removed by a clean-up team.
Maritime New Zealand is encouraging people to sign up to its Adopt-a-Beach programme, to look after beaches in their area.