At least nine dolphins have been slaughtered in the Japanese town of Taiji, activists have said.
The dolphins were the first to be killed since the hunting season started in the country last August.
Activists from the Sea Shepherd Conservation Society, who call themselves "Cove Guardians", reported the slaughtering on Tuesday morning.
"First pod of 2014-2015 being driven into cove now," they tweeted at 10.33am local time.
About one hour later, they wrote: "First dolphin murder of the drive hunt season is complete as dead bodies are dragged to Taiji butcher house."
Activists also streamed live footage of a bay where dolphins were corralled and killed.
Animal rights advocate Zoe Ng told the South China Morning Post, "Today a pod of Rissos were murdered at the Cove.
"We're frustrated beyond words. "This year [the fishermen] hide behind tarps and still carry on their brutal murderous ways."
According to the charity Whale and Dolphin Conservation (WDC), some 850 dolphins of mixed species were killed in the hunts in 2013, while more than 150 were taken alive for captivity.
A similar number of dolphins is expected to be killed or captured this year.
On the same day Japan announced the beginning of the hunting season, animal rights advocates in Japan marked Japan Dolphin Day and demonstrated against the hunting season which, according to the protesters, is not part of the tradition of Japanese people.
The issue of dolphin hunting in Japan sparked international outrage after the release of the 2009 documentary The Cove, directed by former National Geographic photographer Louie Psihoyos, which shows the capture and slaughter of some dolphins during the hunting season.
The documentary claims that more than 20,000 dolphins and porpoises are killed every year in Japan.
The Cove prompted hundreds of activists worldwide to protest against the hunting, with some demanding Japan to be banned from hosting the 2020 Summer Olympics.