Japanese whaling vessels have reportedly departed for the Southern Ocean on their annual hunt.
Citing the Fisheries Agency, Kyodo News reported three vessels had departed from the far-western port of Shimonoseki.
Environmental group Greenpeace said the mother ship had left another port also in the country's west.
"Nisshin Maru left Innoshima today," Greenpeace Japan's executive director Junichi Sato said.
"Today was virtually the last day when they could leave for the Antarctic sea."
Kyodo said the Nisshin Maru would join the three vessels that left Shimonoseki earlier in the day.
Japanese authorities refused to confirm either departure.
"We do not disclose when the vessels leave or left for safety reasons," an agency official said.
The fleet plans to hunt up to 935 Antarctic minke whales and up to 50 fin whales through March.
The fleet's departure comes weeks later than expected and days after a US court ordered environmental group Sea Shepherd to stay at least 500 metres from whaling vessels after a complaint from Japan.
Sea Shepherd, led by captain Paul Watson, each year disrupts the expeditions.
In a statement on its website, Sea Shepherd called the US court ruling "the first shot of the season" by Japanese whalers.
Confrontations between the whalers and activists have escalated in recent years, and the Japanese cut their hunt short in early 2011 due to Sea Shepherd harassment.
Japan hunts whales using a loophole in a global moratorium that allows killing the sea mammals for what it calls "scientific research", although the meat is later sold openly in shops and restaurants.
Sea Shepherd's ninth campaign, named Operation Zero Tolerance, is its largest ever against Japan's whale hunt and involves four ships, a helicopter, three drones and more than 100 crew members.
Three of the vessels, the Steve Irwin, Bob Barker and Brigitte Bardot, are all at sea while the Sam Simon is at an undisclosed location.