A conservation group's high-tech boat had its bow sheared off in a collision with a Japanese whaling ship in Antarctica.

The $1.5m, 79 foot long 'stealth' boat Ady Gil sank after the collision in Southern Ocean but its six man cew was rescued uninjured, said Captain Paul Watson, founder of the radical environmental group Sea Shepherd.

Captain Watson said the Ady Gil was idling in Antarctic waters when it was suddenly rammed by the Japanese ship Shonan Maru, which was providing security to Japan's whaling fleet.

The clash was apparently the most serious in the past several years, during which the group has sent vessels into far southern waters to try to harass the Japanese fleet into ceasing its annual whale cull.

Clashes using stink bombs, ropes meant to tangle propellers and hi-tech sound equipment have been common in recent years, and collisions between ships have sometimes occurred.

The society said its boat Ady Gil - a speedboat which resembles a stealth bomber - was hit by the Japanese ship the Shonan Maru near Commonwealth Bay and had its bow sheared off.

"The condition of the Ady Gil now is that it is inoperable and the crew of the Ady Gil has been transferred to our other vessel, the Bob Barker," Locky Maclean, the first mate of the society's lead ship said.

The Ady Gil's captain had stayed on board to try to save equipment from the boat "before it floods too severely," he said.

Japan's Fisheries Agency, which has no direct involvement in whaling but overseas all the country's fishing operations, said it was still checking details about the clash.

"We have confirmed that there was a collision, but we have no other details. We have not heard that any boats have sank. We are now trying to confirm details of why the collision occurred," said Fisheries Agency spokesman Toshinori Uoya.

Mr Uoya said there were no injuries on the Japanese side, but said he was not sure about the Sea Shepherd crew members.

PA Media