An anti-whaling group says its ships are in pursuit of a Japanese fleet whose crews it alleges have killed four protected whales in New Zealand's territorial waters.
Sea Shepherd New Zealand spokesperson Michael Lawry said on Monday that the group would try to drive the whalers away from the area.
The three-vessel Sea Shepherd fleet comprising the Steve Irwin, the Bob Barker and the Sam Simon found five whaling ships in New Zealand waters in the Ross Dependency Antarctic region.
The area is inside the Southern Ocean whale sanctuary, where commercial fishing is banned under International Whaling Commission (IWC) rules.
Michael Lawry said a Sea Shepherd helicopter spotted the Nisshin Maru and filmed three dead minke whales on its deck while a fourth was being cut up. He said that is proof of Japan's illegal hunt.
"There's three whales that were waiting to be butchered. The fourth one had already been cut up and there was blood smeared right across the deck. The outlaw whalers on board were hauling body parts with hooks and chains and some stuff was obviously going to be thrown overboard as well."
Glenn Inwood, a spokesperson for Japan's Institute of Cetacean Research, dismissed the group's claims.
"Nothing that emanates from the Sea Shepherd propaganda machine is ever correct. Secondly, the minke whales that Japan is taking are under the research programme on behalf of the government of Japan are in no way endangered - they are quite abundant, they are numerous and they're certainly not protected."
Mr Inwood said Japan has a legal right to whale in the region and has proven to the IWC that its work is purely for research purposes and falls outside the ban.
But Sea Shepherd said the fleet will do what it can to ensure that no more whales are killed. "Sea Shepherd will remain relentless in driving these fake, desperate and subverting 'scientists' back to Tokyo," Steve Irwin captain Sid Chakravarty said.