An Air Force Orion has been observing a protest flotilla in the sea off East Cape at the request of police.
The surveillance plane was sent after the Government asked police to monitor the protest.
Greenpeace activists, supported by members of a Maori iwi, are disrupting a search for oil and gas by Petrobras.[image:1675:half:right]
The Brazilian oil giant is conducting a preliminary seismic survey of 12,000 square kilometres of sea bed off the east coast of the North Island.
Petrobras has a permit to explore the area to determine if oil or gas are likely to be under the ocean floor in commercial quantities.
It has a licence to search for oil and a legal obligation to continue under the terms of an agreement with the Crown.
However, operations have been halted since Sunday when Greenpeace began protesting and put swimmers in front of survey ship the Orient Explorer in waters of the Raukumara Basin.
Greenpeace says deep sea oil production is environmentally risky and has sent five yachts and a fishing boat to disrupt the search.
Police say they will act only if what they call "unlawful actions" occur and have a range of assets at their disposal, including planes and naval vessels.
Greenpeace says its protest is peaceful and there is no justification for calling police.
Safety a concern, say police
National manager of operations Superintendent Barry Taylor says everyone has the right to carry out lawful protest and the surveillance plane is there to monitor actions on the water.
Mr Taylor says police are looking at whether more needs to be done.
"We are still assessing what may be ahead of us. We are very hopeful that there will be no further action on behalf of the protesters.
"We fully acknowledge that everyone has the right to lawful protest - but then again, the survey company also has the right to carry out their own lawful business."
Mr Taylor says police have an obligation to ensure the safety of New Zealand citizens and having people in the water 35 nautical miles offshore is a risk.
Government urged to step in
The oil industry says the police must do more than just monitor the protesters.
John Pfahlert, executive officer of the Petroleum Exploration and Production Association, says urgent action is needed.
"The Government really needs to now step in and ensure that Petrobras has the ability to continue with their survey, whether that's involving the police or the Navy to intervene.
"Clearly, the actions of Greenpeace are really nothing more than an attempt to sabotage New Zealand's economic growth."
Prime Minister John Key says the Government is seeking legal advice on the powers police have to intervene in the protest.
Mr Key says Petrobras has a legal right to carry out exploration work within New Zealand's economic zone and Greenpeace has a right to protest.
However, he says the protest is preventing Petrobras from carrying out its work and if that was happening on dry land, police would be able to do something about it.