An application to mine South Taranaki's iron sands has been granted, despite acknowledgement there could be "100 per cent loss" of marine life on the sea floor.
Trans-Tasman Resources applied to extract 50 million tonnes of material from the seabed off Patea and export five million tonnes of iron sand every year for 35 years.
The mining is worth an estimated $1.1 billion a year to the value of goods and services produced in New Zealand.
The proposal to mine ironsand from 66 square kilometres of seabed offshore from Patea received 13,733 submissions, most opposed to granting consent.
The application was considered by the Environmental Protection Authority (EPA), which held hearings in Wellington and Taranaki and delivered a majority decision today.
EPA chief executive Allan Freeth announced the consent, at a briefing held in Wellington.
He said the application had been among the most challenging and complex the EPA had ever dealt with.
There would be "significant" impacts on marine mammals, fish, and creatures that lived on the sea floor.
That included a sediment plume that could spread three kilometres, and would reduce light, and possibly smother marine creatures.
"The impact on benthic [sea floor] life within the mining site, while being expected to be a 100 per cent loss in the short term, is expected to be temporary in the view of the majority [committee] decision," Freeth said.
"Conditions have been imposed to monitor this recovery, and take steps to ensure it occurs over the medium to long-term.
"While marine mammals may be affected by the sediment plume, the greater potential impacts will arise from noise produced by the mining vessels.
"Noise at a level likely to cause behavioural impacts will extend for some considerable distance in all directions."
Freeth said commercial, recreational and customary fishing may also be affected, as fish were likely to avoid the area.
"I acknowledge the decision outcome is likely to be a difficult one for all involved.
"The fact that the [committee] members disagreed reflects the complexity of the issue."
Freeth said the committee had weighed up benefits and possible negative impacts, and had imposed conditions to try to mitigate impacts.
He said there were expected economic benefits including 1600 jobs across New Zealand, and to the shareholders of Trans-Tasman Resources.
Appeals can be lodged with 15 days of today's decision.
Ngati Ruanui has announced it plans to appeal, as has Kiwis Against Seabed Mining. That would send the decision to the High Court.
Ngati Ruanui spokesperson Debbie Ngarewa-Packer said the fact that the EPA's own committee was divided on the decision showed appealing was the right thing to do.
"If you're not united in a decision like this, then something's wrong.
"We will be lodging an appeal based on the process, and the lack of compliance, the lack of information they took into consideration, and the fact that they didn't reach unanimous consensus.
"The Act says they have to be beyond any doubt before they bring anything into our backyard."
KASM chairman Phil McCabe said the group had little choice.
"We have to take the only responsible route here by appealing this decision, on behalf of the future of our coastal peoples and environment, the blue whales, maui dolphins and little penguins.
"We saw at least 13,700 people object to this proposal, and the only logical next step is to challenge that decision on their behalf," said McCabe.
"We are stunned that the EPA could have given this experimental industry the go-ahead, given the startling lack of available crucial information. Even the EPA's decision making committee was split on its decision, requiring an extra vote from the Chair. We have no choice but to lodge an appeal," he said.
The west coast of the North Island has some of the largest ironsand deposits in the world, stretching 480km from Kaipara to Whanganui.
Kiwis Against Seabed Mining (KASM), Greenpeace, local tribe Ngati Ruanui, and Forest and Bird opposed the application.
The Ministry for Business, Innovation and Employment supported the application, saying New Zealand has been mining iron sands since the 1960s.
Giving consent to Trans-Tasman Resources would add wealth to the country, encourage overseas investment and further the Government's growth agenda, the ministry submission said.
With iron ore valued at US$40 to US$50 a tonne, the Government would get an extra $7 million in royalties each year, doubling its total from mining.
The worth of annual exports would increase by $312 million to $350 million.
- Additional reporting by Newstalk ZB