Environmentalists and nationalists held opposing rallies over the issue of Japan's dolphin and whale hunts in a rare showdown in central Tokyo on Saturday, leading to angry scenes.

About 50 anti-whaling activists gathered at a park in the Shibuya shopping district with banners bearing slogans such as "Stop the cruel dolphin hunt!" while across the street about 30 nationalists shouted "Get out of Japan!"

The nationalists accused the environmentalists of undermining Japanese culture and traditions, saying "environmental terrorists" should be sent to slaughter houses.

The rally was part of demonstrations to be held around the world this weekend against the killing of dolphins in the Japanese town of Taiji, according to the organiser, Action for Marine Mammals.

Demonstrations are also planned in cities including London, Sao Paulo, Vancouver and across the United States, the Tokyo-based group said.

Taiji, in western Japan, drew global attention after "The Cove", a hard-hitting film about the annual dolphin hunts there, won the Academy Award for best documentary in 2010.

Fishermen corral hundreds of dolphins into a secluded bay, select a few dozen for sale to aquariums and slaughter the rest for meat. The dolphin hunt takes place over a period of months.

The demonstrators also called for an end to Japan's annual state-sponsored whaling mission to the Southern Ocean, due to start in the next few weeks.

Japan hunts whales using a loophole in a global moratorium that allows for so-called "scientific research", although the meat is later sold openly in shops and restaurants.