Japanese whaling ships left port Thursday for Antarctic waters for the annual hunt of the ocean giants, Greenpeace said, setting the stage for high-seas confrontations with anti-whaling activists.

The factory ship Nisshin Maru and the smaller Yushin Maru 2 and 3 left the western port of Innoshima shortly after 10am (0100 GMT) for what is usually a five-month voyage, said the environmental activist group.

Japan kills hundreds of whales a year in Antarctic waters by using a loophole in the 1986 moratorium on commercial whaling that allows the sea mammals to be hunted for "lethal research."

Anti-whaling nations led by Australia and New Zealand and environmental groups have attacked Japan for its annual whaling expeditions, criticizing them as cruel and unnecessary.

Japan, which says whaling is part of its culture, makes no secret of the fact that whale meat ends up on dinner tables.

Militant activists, especially the Sea Shepherd Conservation Society, have harassed whalers in recent years, moving their ships and inflatable boats between the harpoon ships and the sea mammals.