Japanese fishermen on Friday killed the first dolphins of the season in a controversial annual hunt that attracted global attention after it was featured in the Oscar-winning 2009 documentary "The Cove".

Fishermen at the western town of Taiji caught 20 dolphins, according to the local Kii Mimpo newspaper.

"We finally caught them. I'm relieved," Yoshifumi Kai, a senior official of the local fisheries association, told Kyodo News agency.

Campaign group Dolphin Project, led by US animal rights activist Ric O'Barry, tweeted that about "12 to 15 Rissos dolphins were slaughtered in the cove".

During the six-month hunting season, people from the southwestern town corral hundreds of the mammals into a secluded bay and butcher them, turning the water crimson red.

The scene was featured in the documentary, drawing unwanted attention to the little coastal community.

Environmental campaigners visit the town every year to watch the gruesome event and authorities have boosted their presence to prevent any clashes between locals and activists.

There were no clashes between ant-whaling activists and fishermen on Friday, Kyodo News added.

Officials and fishermen at Taiji could not be reached for immediate comment.

Defenders of the hunt say it is a tradition and point out that the animals are not endangered, a position echoed by the Japanese government.

Ric O'Barry, the star of "The Cove", was detained earlier this year for nearly three weeks after being denied entry to Japan, and was deported from the country.