While the vessel has stowed arms below deck to avoid a confrontation, Australian customs officials on board will gather photographic and video evidence of the Japanese kill.

Japan's whaling fleet plans to hunt 935 minke whales and 50 fin whales for research over the Antarctic summer, but recently abandoned plans to hunt 50 humpback whales after international condemnation and a formal diplomatic protest by 31 nations.

Australia also plans to use patrols by a low-flying A319 Airbus jet used by Australian Antarctic scientists to follow and photograph the Japanese fleet, intensifying pressure on Tokyo to end the hunt in future. This year's cull ends in February.

Japan has long resisted pressure to stop scientific whaling, insisting whaling is a cherished cultural tradition. Its fleet has killed 7,000 Antarctic minkes over the last 20 years.

"We are conducting our research in accordance with the international treaty on whaling, and therefore we will never change our stance," an official at Japan's Fisheries Agency said after the Australian ship departed.

The ship is expected to take at least a week to reach the whaling grounds and Australia's government is refusing to comment on its movements, sparking criticism from anti-whaling activists hoping to disrupt the fleet's operations.

Foreign Minister Stephen Smith said photographic evidence gathered by the Oceanic Viking and aircraft could be used before tribunals including the International Court of Justice in The Hague and the International Tribunal for the Law of the Sea to stop Japan's hunt.

The Japanese official said a case would never succeed.

"Antarctica is not a territory of any country. Lawful activities in open seas can never be blocked," he said.