The grounding of the Rena container ship off Tauranga last year will cost taxpayers $50 million, it has been revealed.

Labour's environment spokesman Grant Robertson has today released documents which show the estimated total costs of the clean-up have blown out from the initial allocation of $25m.

Papers show Transport Minister Gerry Brownlee wrote to Parliament's economic growth and infrastructure committee earlier this year requesting approval for a $10 million funding boost. And he notes further funding ''is also likely to be required.''

''Kiwis have seen the heart-breaking environmental cost of the grounding. Now we know the total price tag for the clean-up will be $50 million, a large part of which Kiwis will be paying for,'' Robertson said.

A spokesman for Brownlee said $50m was ''an upper end estimate'' used in the Cabinet paper. ''The actual cost to date is closer to $40m.''

''There are on-going negotiations with the Rena's owner/insurer with regard to recovering the Crown's costs,'' he said.

The Rena ran aground the Astrolabe reef in October, leaking around 350 tonnes of oil and sending containers toppling into the sea. At the time it was described as New Zealand's environmental disaster.

In January, the Greek owned ship snapped in half but the vessel remains on the reef. Salvers began removing sections earlier this week.

Robertson requested the documents from Maritime NZ, the government agency responsible for the response operation.

He called on the government to incorporate international conventions on liability for damage into New Zealand law.

In 2008, the incoming National government was advised by a parliamentary select committee to complete the legislative work.

"If National had... costs to taxpayers would have been significantly reduced,'' Robertson said.

Fellow Labour MP Phil Goff has now proposed the legislation as a Member's Bill.

"The government should pick this up or get off its backside and introduce its own legislation. Otherwise, if another accident happens, taxpayers will be forking out again. It is simply not good enough," Robertson said.

Around $25 million was initially set aside for the clean-up, with another $2 million coming from the Oil Pollution Fund.

Mediterranean Shipping Company, the firm which chartered the vessel, also offered $1 million, although this is yet to be paid.

In the documents it is noted: ''This is an incident of unprecedented size and difficulty in New Zealand's maritime history.

''Responding to an incident of this size and nature goes well beyond the usual capacity and financial capabilities of Maritime New Zealand.''

Initial estimates from the environment ministry suggest $3.2 million will be needed for a long-tern environmental recovery plan.

- © Fairfax NZ News