A Greenpeace member was thrown overboard into the icy ocean waters by the tow rope on the Japanese harpoon after it flew past their inflatable boat on Saturday, officials from the environmental watchdog said.

The harpoon flew within a meter (yard) of the Greenpeace Zodiac and killed the minke target, while activist Joe Constantine was able to climb back aboard the boat to safety, the group said.

It was the latest in a string of incidents since Greenpeace boats began shadowing a Japanese whaling fleet late last month in a bid to halt the killing of whales in the Antarctic Ocean.

Greenpeace spokesman Shane Rattenbury said the protesters had prevented the ship from harpooning the minke whale for more than a hour during Saturday's confrontation, but the Japanese then fired in what he called a dangerous escalation of the standoff.

"Yesterday took it to a new level -- we are very concerned about that," Rattenbury said on Sky News television.

"There is definitely an increasing level of tensions down here and the harpooners are certainly starting to take shots that perhaps a week or two weeks ago they would not have taken," he said.

"So it is certainly forcing us to think about our tactics and we might have to look at a different way of doing things."

A week ago the Greenpeace ship Arctic Sunrise collided with the Japanese whale processing ship Nisshun Maru in the Antarctic and both sides accused the other of responsibility for the crash.

Greenpeace claimed a video of the incident showed the Japanese vessel failed to give right of way to their ship, while Japan's Institute for Cetacean Research asserted the activists deliberately rammed their ship "to get media coverage".

The International Whaling Commission imposed a moratorium on commercial whaling in 1986 but Japan has continued hunting for what it calls scientific research.

Japan, however, makes no secret that the meat from the hunt winds up on dinner plates.

Rattenbury said the increased risks being taken by the Japanese harpooners showed the Greenpeace campaign was working, but he stressed that more action from governments was needed to halt Japan's whaling program.

"There is a limit to what Greenpeace can do down here, and as the risks increase we really need to see the anti-whaling governments around the world take stronger action to bring this hunt to an end so we don't have to be putting ourselves in the firing line any more," he said.

"It's quite clear that this is not about scientific research -- you don't need to kill a whale to study it.

"This is just commercial whaling in disguise."

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