A space-age powerboat sent to harass Japanese whalers was rammed and sliced in two in its very first clash yesterday, activists said, dramatically escalating hostilities in icy Antarctic seas.

The futuristic Ady Gil trimaran, which holds the round-the-world speed record for a powered vessel and was enlisted by activists from the Sea Shepherd Conservation Society for this whaling season, received "catastrophic damage" and was sinking, they said.

All six crew, who earlier hurled stink bombs at the whalers to disrupt their annual hunt, were rescued unharmed by Sea Shepherd's Bob Barker ship.

Activists described the collision as unprovoked but Japan lashed out at the the group, accusing them of "extremely dangerous" behaviour.

"The Shonan Maru No.2 suddenly started up and deliberately rammed the Ady Gil, ripping eight feet (2.4 metres) of the bow of the vessel completely off," a Sea Shepherd statement said.

"The Ady Gil is believed to be sinking and chances of salvage are very grim," it added.

But the Japanese Fisheries Agency said the Ady Gil came abnormally close to the Shonan Maru No.2 and suddenly slowed down while crossing in front of it. "These acts of sabotage that threaten our country's whaling ships and crew were extremely dangerous," it said in a statement. "It is totally unforgivable."

Videos released by both the Japanese and the activists show the sleek, black powerboat and the Shonan Maru No.2 colliding as the whaling ship targets it with water cannons. There was no major damage to the Japanese ship and no Japanese crew members were injured in the collision, the fisheries agency said.

The whalers accused the Ady Gil's five New Zealand and one Dutch crew of trying to tangle the Nisshin Maru's rudder and propeller with rope, and aiming a "green laser device" at its sailors, as well as launching stink bombs.

"The Sea Shepherd extremism is becoming more violent... Their actions are nothing but felonious behaviour," Japan's Institute of Cetacean Research said in a statement. Sea Shepherd activists have harassed the Japanese fleet over the past six hunting seasons and claim to have saved the lives of hundreds of whales.

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