Sea Shepherd said Japanese whalers deliberately crashed into their vessel, while the Japanese government said the conservation group tried to sabotage its research fleet, the Australian Broadcasting Corp. said.
"The Sea Shepherd ships Steve Irwin and Bob Barker were both unprovokedly attacked by three harpoon ships belonging to the Japanese whale poaching fleet," Capt. Peter Hammarstedt of the Bob Barker told the ABC. "These harpoon ships came in heavy and hard."
The collision resulted in significant damage to the Bob Barker.
The Japanese Institute of Cetacean Research said the activists dragged ropes in front of the Japanese fleet and rammed into one of their ships.
The government said it is seeking more information about the collision.