Japan's whaling fleet has left port for the country's annual hunt in Antarctica, according to local media reports.
Three ships, led by the 720-tonne Yushin Maru, set sail from Shimonoseki in western Japan on Tuesday.
The government's fishery agency declined to confirm the reports on Tuesday, citing security reasons, AFP reports.
In February this year, Japan cut short its hunt for the 2010-2011 season by one month, blaming interference from the American-based environmental group Sea Shepherd Conservation Society.
The fleet caught 172 whales, about a fifth of its planned catch.
This season, according to a plan submitted by the government to the International Whaling Commission, it aims to catch about 900 minke and fin whales.
Commercial whaling is banned under an international treaty but since 1987 Japan has used a loophole to carry out "lethal research" on the mammals in the name of science.
Japan claims it is necessary to substantiate its view that there is a robust whale population in the world and makes no secret of the fact that whale meat from this research ends up on dinner tables and in restaurants.
Anti-whaling nations and environmentalist groups routinely condemn the activity as a cover for commercial whaling.
In October, Australia and New Zealand renewed their demands that Japan abandon its plan to return to the Antarctic Ocean.
New Zealand Foreign Affairs Minister Murray McCully said at the time the plan was "entirely disrespectful of the strong concerns expressed by Australian and New Zealand people, for whom the Southern Ocean is our neighbourhood".