Australia will take diplomatic action to encourage Japan to drop its "scientific whaling" program, amid reports the Japanese fleet has begun its journey south.
Environment Minister Tony Burke has restated the government's strong opposition to Japan's whaling expeditions and dismissed Japanese claims that the program is for scientific research.
"There is nothing scientific about going out and chasing whales, aiming a harpoon at them, so that you can pull them in and chop them up for food," Mr Burke told reporters in Sydney on Saturday.
Australia would lobby Japan to respect a moratorium on whaling in the Southern Ocean, taking "all diplomatic action that a government can take", he said.
But Mr Burke said the government would not respond to Coalition calls for a customs vessel to be sent to the Southern Ocean to monitor the annual whale hunt.
"The information that we have on the way Japan has alternated this each year is that in all likelihood they'll be in the New Zealand search-and-rescue zone anyway," he said.
Opposition environment spokesman Greg Hunt on Monday wrote to Prime Minister Julia Gillard saying it was vital an Australian vessel be present in case of any clashes between Japanese whalers and the anti-hunt group Sea Shepherd.
"There is a real risk of conflict or collision causing injury, death or a major environmental spill in the event of a sinking," Mr Hunt said.
Greens acting leader Adam Bandt says the government should seek a court injunction to stop the whaling.
"The government says it wants to do something about it and has commenced proceedings in the court, but it hasn't done the simple thing that would actually stop the whaling, and that is go off and seek an injunction," Mr Bandt told reporters in Melbourne.
The Australian government started legal proceedings at the International Court of Justice in May 2010.
Both Australia and Japan have filed their detailed written arguments to the court and the case has been set down for oral hearing at The Hague, probably next year.
Attorney-General Nicola Roxon said the decision to start legal proceedings was not taken lightly.
"The Australian government considers Japan's whaling program is contrary to its international obligations and should stop," Ms Roxon said.
Citing the Fisheries Agency, Kyodo News reported on Friday three vessels had left from the far-western port of Shimonoseki, while environmental group Greenpeace said the mother ship had left another port, also in the country's west.
The fleet plans to hunt up to 935 Antarctic minke whales and up to 50 fin whales through March, the fisheries agency said earlier.
The Australian government had not yet received official confirmation that Japan's annual whaling hunt was beginning, and did not expect to.
"Last year there was no stage when the Japanese government actually confirmed its whaling fleet was heading south," Mr Burke said.