Greenpeace is heading to court to try to stop Texan oil giant Anadarko drilling off the coast of New Zealand after calling off its sea protest.
The legal challenge to the Environmental Protection Agency (EPA) decision was filed in the High Court at Wellington on Tuesday, a few hours after Anadarko started exploratory drilling off the Raglan coast.
Greenpeace says the EPA made an error in law by allowing Anadarko to drill without looking at several key documents, including reports on oil spill modelling and emergency plans to deal with an oil spill.
It wants an urgent hearing date because it says the issue is of national importance.
Greenpeace chief policy advisor Nathan Argent says a successful challenge could halt Anadarko's drilling, which began at 2.30am (0030 AEDT).
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"The government's process appears to have a hole in it so big that an untested 230m-long drilling ship has been driven through it."
Mr Argent said that not only had Greenpeace not seen the documents relating to oil spilling, it appeared government ministers and the EPA hadn't seen them either.
"This not only looks shockingly lax, and a complete contrast from government claims that oil companies have been put through the wringer, it also now looks like this was not lawful."
A number of vessels have been protesting at the site of the drilling operation, about 160km off the coast, but Greenpeace executive director Bunny McDiarmid says she will be leaving to concentrate on the court challenge.
The Greenpeace ship Vega has been inside the 500m safety exclusion zone since Anadarko's drilling ship, the Noble Bob Douglas, arrived at the site last week.
Anadarko spokesman Alan Seay said the early morning drilling start had nothing to do with Greenpeace's protest.
Green Party energy spokesman Gareth Hughes says Anadarko should cease drilling until the court case is decided.
