Environmental campaigners from the Sea Shepherd group say a Japanese whaling ship had rammed their vessels in the worst confrontation in the Southern Ocean in three years.
Sea Shepherd said the Japanese factory boat the Nisshin Maru had deliberately collided with the vessels Steve Irwin and Bob Barker, which were crewed by anti-whaling campaigners.
The incident came as the Australian-flagged Sea Shepherd ships tried to block the Nisshin Maru from reaching the whaling fleet's tanker ship, the Sun Laurel, for refuelling. Sea Shepherd's co-campaign leader Bob Brown described the collisions as "the most outrageous attack on the Sea Shepherd Australia ships today; multiple rammings of those ships by the giant factory whaling ship from Japan".
"Water cannon laid on the ships and concussion grenades lobbed on the ships from the Japanese government escort vessel," Brown said. "Japan through its loud hailers... ordered Australian ships out of Australian territorial waters while they wanted to proceed with their illegal refuelling of the Nisshin Maru ... to allow them to continue their illegal whaling in this international and Australian whale sanctuary."
Brown said the incident had destroyed a lifeboat on the South Korean tanker the Sun Laurel.
He said it was the worst confrontation since a collision in January 2010 that caused the campaigners' vessel Ady Gil to sink.
Sea Shepherd said the Nisshin Maru rammed the Bob Barker several times, including from behind, destroying one of their radars and all of their masts. The incident caused the Bob Barker to lose all power and issue a distress call. Power has since been restored to the ship.
"It's extraordinarily dangerous and it's just a direct break of international law," said Brown, the former leader of Australia's Greens party. "Canberra needs to tell Tokyo to haul off immediately and to dispatch naval vessels down there to uphold international law."
Sea Shepherd's Jeff Hansen said the Steve Irwin had been struck on the stern and right hull.
"We're now under attack with concussion grenades being thrown by armed Japanese coastguard in Australian waters at our crew," he told ABC television. "We're very concerned for the safety of our crew.
An official at the whaling division of the Japanese government's fisheries agency said it was checking the allegations.