A Japanese whaling fleet set sail for the Antarctic today after a one-year pause, with environmentalists criticising the move as a "crime against nature".

Government officials and families of crew members stood on the quayside and waved as ships - at least one fitted with a powerful harpoon - left a southern port.

"Two whaling ships departed from Shimonoseki with a Fisheries Agency patrol boat this morning, while the factory ship also left another port to form a fleet," an agency official said.

"A fourth whaler already left a northeastern port yesterday to join the fleet."

Despite worldwide opposition, Japan persists in hunting whales for what it says is scientific research.

The move came after a one-season suspension of its hunting in the ocean as the United Nations' top legal body judged last year that Japan's scientific whaling was a cover for a commercial hunt.

In response, Japan's 2014-15 mission carried out only "non-lethal research" such as taking skin samples and doing headcounts.

Japan makes no secret of the fact that the animals' meat ends up for sale

Japan's fisheries agency has since told the International Whaling Commission that it would resume whaling in the Antarctic Ocean by cutting annual minke whale catches by two thirds to 333 this season.

But the IWC's scientific committee said in June that Japan had failed to give enough detail to explain why it wanted to kill almost 4,000 minke whales in the Antarctic over the next 12 years.

Tokyo claims it is trying to prove the whale population is large enough to sustain a return to commercial hunting and says it has to kill the mammals to carry out its research properly.

However, Japan makes no secret of the fact that the meat ends up for sale.

The government has said for months it intended to resume butchery in the current season, which runs to around the end of March.

The announcement that the hunt was to resume drew condemnation from around the world.

Claire Bass, executive director for Humane Society International, said Japan had chosen to ignore the "universal opposition".

"Once again we have Japan's whaling fleet setting sail to commit a crime against nature," she said in a statement, stressing "Japan's long history of whale persecution".

Other conservationists called for another legal challenge.

The International Fund for Animal Welfare and the Australian Marine Conservation Society said a panel of legal experts had been asked to consider Japan's latest whaling mission had found it broke international law.

"The panel concluded that Japan's new whaling programme violates international law and that Australia or other countries still have options to challenge Japan's actions before international courts," said chair and Australian National University professor Donald Rothwell.