Activists from Sea Shepherd Australia have found the Japanese whaling fleet and disrupted the hunt, renewing the Antarctic conflict.
The Nisshin Maru was found processing harpooned minke whales in waters south-east of Tasmania near the Balleny Islands on the edge of the Ross Sea, the group said.
It said it had located all five vessels of the Japanese fleet, and now had them on the run.
A Sea Seaherd helicopter has collected graphic images of whales being processed on the deck of a Japanese vessel in waters south-east of Tasmania. Photo: Tim Watters/Sea Shepherd
"Once again, the Japanese government has shown flagrant disregard for international law by continuing their illegal whale hunt while the world patiently awaits a decision from the International Court of Justice," said Peter Hammarstedt, captain of the Bob Barker.
The activists located the whaling fleet on Sunday night and a pursuit of the Nisshin Maru was continuing on Monday, a spokesman for the group said.
''We've got a helicopter over them now,'' the spokesman said.
An earlier flight by the group's helicopter collected graphic images of whales being processed on the deck of the factory ship.
Sea Shepherd Australia's managing director, Jeff Hansen, said the International Whaling Commission's Southern Ocean Whale Sanctuary was being tainted by the illegal slaughter of these whales.
''One thing is for sure, Sea Shepherd will do whatever it takes to ensure no more whales have to endure pain and suffering at the hands of these whale butchers from Japan."
The encounter confirms the opening of hostilities between the two sides for the 10th whaling season. There were repeated collisions between the vessels in ice strewn polar waters off Australia's Davis base last year.
The Japanese consul-general in Melbourne, Hidenobu Sobashima, told Fairfax Media that unlawful violent activities by Sea Shepherd against vessels engaged in research whaling were ''inadmissable''.
''The government of Japan has repeatedly requested the government of Australia, as a flag state and a port of call by Sea Shepherd vessels, to take effective measures to ensure the safety of navigation at sea, and hopes such specific measures will be taken," Mr Sobashima said.
This summer's conflict will take place without observation and monitoring by an Australian Customs ship after Environment Minister Greg Hunt failed to deliver on an election promise to send a vessel south.
Instead Mr Hunt said an Australian Antarctic Division Airbus A319 would make unannounced flights over the whaling fleet.