Japan has warned it may send armed aircraft to defend its whaling ships in the Southern Ocean if clashes with protest boats escalate.
The whaling nation also says it may ask Australia to take action against protesters.
The increasingly tense conflict prompted a Green Party call last night for New Zealand to send a frigate to Antarctica in a monitoring role - an option the Government quickly ruled out.
The confrontation with the whalers intensified yesterday, with conservation group Sea Shepherd threatening to ram and disable the Japanese whaling fleet.
The group's ship, Farley Mowat, is equipped with a blade device - known as the "can opener" - mounted on its side and designed to rip open a ship's hull.
Sea Shepherd's threat came as Japan's Fisheries Agency said it was considering asking its Maritime Police Agency to send armed aircraft to defend the whaling ships.
The Melbourne Age, which reported the proposal, described it as using "quasi-military aircraft under the guise of the police to quell a civilian protest".
The newspaper also reported that the agency might ask the Australian Government to act against Greenpeace - a separate organisation from Sea Shepherd - to "normalise the situation".
Two New Zealanders are among the Greenpeace protesters in vessels chasing the whalers. There are three New Zealanders on Sea Shepherd's ship.
New Zealand and Australia share strong anti-whaling views. Japan says the whaling is necessary for research.
Greens leader Jeanette Fitzsimons urged the New Zealand Government to send a frigate to monitor events in the Southern Ocean.
"New Zealand has taken a strong position against the resumption of commercial whaling, but now it is time to stand up and be counted the way we did when we sent the frigate to Mururoa Atoll in 1973.
"New Zealand had the courage to take action then and it should do the same now."
But Conservation Minister Chris Carter said a frigate would be unlikely to help the situation and instead urged the whalers and the protesters to act responsibly.
"Show restraint and act responsibly because this is a very dangerous part of the world and it would be very difficult to effect a rescue if people got into danger down there."
Duty minister Phil Goff also said there would be no role for a Navy ship.
"We have no legal authority over either party. Sending a frigate down there would serve no purpose because we would have no authority to act as intermediaries between the protesters and the whalers."
The Greens have also joined the Australian Green Party in calling for their respective Governments to stop Japanese whalers, military and police using New Zealand and Australian ports and airports.
"Japan is flouting international agreements and public opinion by escalating its slaughter of whales, especially when everyone knows their claims of scientific research are just an excuse to get fresh whale meat on to Japanese dinner plates," said Ms Fitzsimons.
Greenpeace has had two ships, Esperanza and Arctic Sunrise, chasing the Japanese fleet across the Southern Ocean Whale Sanctuary since December 21 in an attempt to stop Japan killing more than 900 minke whales and 20 fin whales.
Greenpeace claims Arctic Sunrise was rammed by the Japanese ship Nisshin Maru on Sunday, leaving it with a dent in its hull and a bent mast.
Sea Shepherd captain Paul Watson said his ship had sideswiped and damaged a Japanese ship to "get our point across".
"The whalers have assaulted whale defenders with water cannons and wooden poles. The whalers have rammed two Greenpeace ships and attempted to ram the Farley Mowat."
Sea Shepherd has been battling whalers since 1979 and in that time has sunk nine illegal whaling ships in port without causing injury.
Mr Watson said he would not try to sink a whaling vessel at sea because it would be "far too dangerous".