Japanese whalers and anti-whaling group Sea Shepherd are each pointing the finger at the other after their boats collided at sea yesterday, the second collision between the pair's boats in just over a month.

In a statement yesterday, Sea Shepherd said its vessel Bob Barker was "intentionally" rammed by Japanese harpoon ship Yushin Maru 3 in Australian Antarctic Territory at 4.09pm (NZT), about 180 miles off Cape Darnley.

Today, Japan's Institute of Cetacean Research (ICR) said Sea Shepherd had rammed the Yushin Maru 3 before activists from the group had hurled projectiles containing butyric acid, or rancid butter, at another of its fleet, the Shonan Maru 2.

ICR said the Bob Barker had been approaching its "whale research mother ship" Nisshin Maru and the Yushin Maru 3 had been manoeuvred to prevent the boats coming into contact.

The Bob Barker then rammed the Yushin Maru 3, which suffered minor damage to its handrail and hull, ICR said.

Sea Shepherd said yesterday the Yushin Maru 3 "intentionally" rammed the Bob Barker, creating a metre-long deep gash in the ship's mid starboard side above the waterline and endangering the lives of crew.

"Four harpoon ships, the Yushin Maru 1, 2, and 3 and Shonan Maru 2, were circling and making near passes to the stern and bow of the Bob Barker," Sea Shepherd said.

The group quoted Paul Watson, skipper of the Steve Irwin, currently en route to join the action, as saying the whalers got away scot-free with the "outrageous" sinking of the Ady Gil last month, after that ship and the Shonan Maru 2 collided..

"They appear to have no qualms about endangering Sea Shepherd crew. What we really need is for the governments of Australia and New Zealand to step up and start enforcing maritime laws in these waters, or who know what the whalers will do next. Australian and New Zealand lives are at risk every day in these waters."