A tense stand-off developed inside the Australian Antarctic whale sanctuary as activists reinforced their blockade of Japanese whalers hunting within it.



In ice-strewn waters on Saturday two Sea Shepherd ships steamed close behind the stern of the factory ship Nisshin Maru as it ran along the Antarctic coast far south-west of Perth.



The group said following a near collision between the two sides over the loading of a whale, that any attempt to load another of the animals onto the Nisshin Maru would be blocked.



"We gave them a heck of a fight," said Peter Hammarstedt, skipper of the Sea Shepherd ship Bob Barker. "Now with our two ships on their stern I think their season is done."



However at least one harpoon ship was free to take whales in the ice-strewn waters, and with more vessels arriving, up to seven ships were set to take up positions in the conflict.



The showdown came after the Bob Barker discovered the Nisshin Maru steaming off Davis station on Friday, and the whalers soon after harpooned a female minke whale.



"Through binoculars we could see the whale breaching," said the 29-year-old Hammarstedt.



"We saw the harpoon fire, the cable tighten. Then it was several minutes before she stopped thrashing about."



The harpooning occurred deep inside the Australian Antarctic Exclusive Economic Zone, which is a designated whale sanctuary, but is not recognised by Japan.



Environment Minister Tony Burke said Australia was opposed to whaling wherever it occurred, but particularly in a whale sanctuary.



"For Japan to choose that as a site is deeply offensive," Mr Burke said. "We condemn the activity Japan is involved with."



The Shadow Environment Minister, Greg Hunt, said the sanctuary kill was disturbing, and underscored the need for an Australian Government vessel to monitor the hunt for safety reasons.



"You simply cannot ignore the risk of tragedy in Australian waters, there should be a Customs vessel, there should be representations in Tokyo."



The female minke was only taken aboard the Nisshin Maru for processing into meat after a tense five hour blockade by the Bob Barker.



Hammarstedt said the blockade was broken when the harpoon ship Yushin Maru No. 2 crossed within metres of the Bob Barker's bow, forcing him to peel away to avoid a ramming.



"It took them about a minute to transfer the whale," Hammarstedt said.



Japan's Institute for Cetacean Research said the Bob Barker steamed within "collision distance" of the harpoon ship.



Following the transfer, the Bob Barker remained half a nautical mile off the stern of Nisshin Maru.



On Saturday reinforcement arrived when the activists' flagship Steve Irwin joined the Bob Barker, and Hammarstedt said no more whales had been taken for 24 hours.



Sailing towards them was the whaling fleet's Korean-owned refuelling tanker, Sun Laurel.



It crossed the 60 degrees South border of the Antarctic Treaty Area, shadowed by the Sea Shepherd ship Sam Simon, which has followed the Sun Laurel for 10 days in an effort to block any refuelling attempt by the fleet.



Stringent environmental laws apply within the treaty area . Sea Shepherd said it had been advised that it was against the law for any ship to refuel at sea below 60 degrees South.



"I think they haver given themselves no other choice but to try," said Hammarstedt. "But it is risky, and illegal."



The stand-off came despite a United States court injunction on the Washington state-based Sea Shepherd Conservation Society, against attacking the whalers, or approaching within 500 yards (457m).



Japan's Institute of Cetacean Research has begun a contempt action against SSCS over an alleged breach of the injunction.



The activists argue that control of the anti-whaling campaign is in the hands of Sea Shepherd Australia, and out of the U.S. court's jurisdiction.



