The Sea Shepherd group said it had no intention of pulling out of the conflict after the $2 million protest trimaran Ady Gil had its bow sheared off in the collision with the whaling ship Shonan Maru No. 2.

"If they think that our remaining two ships will retreat from the Southern Ocean Whale Sanctuary in the face of their extremism, they will be mistaken,'' said Sea Shepherd leader Paul Watson. ''We now have a real whale war on our hands.''

The Japanese Government blamed the protesters for the collision, accusing them of sailing too close to the whaling ship and suddenly slowing while crossing in front of it.

''These acts of sabotage that threaten our country's whaling ships and crew were extremely dangerous,'' Japan's Fisheries Agency said. ''It is totally unforgivable.''

Mr Watson denied the Ady Gil crew had been the aggressors, saying the trimaran was idle in waters near Commonwealth Bay, off the Adelie Coast of Antarctica, when it was suddenly rammed by the Japanese ship.

Video footage released by Japan's Institute of Cetacean Research last night showed the Ady Gil gradually increasing in speed into the path of the Japanese ship, countering the Sea Shepherd claim that the Ady Gil was not moving when it was hit.

Australian Environment Minister Peter Garrett said the Government wanted more information about the incident before commenting on its cause.

However, acting Prime Minister Julia Gillard hit out at Japan over yesterday's revelation in The Age that its whalers had organised spy flights from Australian airports to track the Sea Shepherd ships.

''I make it very clear on behalf of the Australian Government we do not condone this action by the Japanese Government,'' Ms Gillard said. ''We are urgently seeking legal advice about the matter to see what our options are.''

Yesterday's collision came after a day of harassment of the whaling fleet by the Ady Gil and a newly-unveiled Sea Shepherd ship, the icebreaker Bob Barker.

In the skirmishing, the Ady Gil's crew tried to entangle the propeller of the factory ship Nisshin Maru but were pursued by Shonan Maru No. 2, which has been deployed to protect the whaling fleet from activists.

The Ady Gil's skipper, New Zealander Pete Bethune, insisted the vessel was stationary and farewelling fellow activists on the Bob Barker when the incident happened.

Mr Bethune told The Age that the 1000-tonne Japanese ship turned toward the 18-tonne Ady Gil from about 75 metres away. ''We though they were going to turn a water cannon on us and I told my crew to brace for that,'' he said. ''Then they T-boned my boat. It was just massive … It's a miracle we all survived.''

The six aboard were uninjured and able to board the Bob Barker from the floating rear section.

''Today is a clear example of how the Japanese don't give a shit,'' Mr Bethune said. ''But this is the end of whaling. You can't go around saying you're trying to conduct scientific research when you're prepared to drive into other people's boats.''

Fellow crew member Laurens de Groot said: ''They were trying to kill us, ramming us like that in one of the most hostile environments in the world.''

Last night the two pieces of the trimaran, formerly the globe-circling Earthrace, were still afloat and the activists were salvaging what they could, including 400 litres of fuel.

An investigation into the incident is to be mounted by the NZ Government, which is the flag state for the Ady Gil.

Coalition environment spokesman Greg Hunt and Greens leader Bob Brown repeated calls for Australia to send a ship south to reassert authority.

The conflict is likely to flare up again within days when Mr Watson's vessel, the Steve Irwin, arrives after refuelling in Hobart.

Mr Garrett said the Government was not making any decision yet about sending a vessel south. ''We will carefully consider whether any additional actions or measures are needed,'' he said.

Mr Hunt and Senator Brown called for legislation to block the logistical use of Australian assets to support whaling activity.