An anti-whaling protest ship collided with a Japanese whaling vessel in the Southern Ocean on Friday as the Japanese tried to haul a dead whale on board, according to an anti-whaling group.
No one was injured in the collision, which caused minor damage to the stern of the Japanese ship, the Sea Shepherd Conservation Society said.
Steve Irwin captain Paul Watson said his ship collided with the Yushin Maru 2 while a dead whale was being pulled up the slipway of the factory ship, Nisshin Maru.
Mr Watson denied that the Steve Irwin deliberately rammed the Japanese ship, saying the Yushin Maru 1 moved directly in front of the Steve Irwin and the collision with the Yushin Maru 2 was "unavoidable".
Mr Watson said the collision crushed a railing at the back of the Japanese ship but there were no reports of injuries.
The Steve Irwin was continuing to tail the Nisshin Maru to prevent whales being hauled on board.
A spokesperson for Japan's Institute of Cetacean Research, Glen Inwood, said the fact the whaling ship was hit with the rear of the protesters' ship suggests it was rammed.
Mr Inwood said though no one was injured this time, someone could have easily been hurt or killed by the action. He said the protesters have been throwing glass bottles of acid onto the Japanese vessels.
The Sea Shepherd Conservation Society has been blamed for collisions with the Japanese Antarctic whaling fleet in recent years, as well as high-seas boardings and stink bomb attacks.
Its confrontational tactics have been widely criticised both by pro-whaling groups and fellow environmentalists, although it has also attracted high-profile supporters.
Mr Watson admits protesters do throw bombs of rancid butter at the whalers to deter them and taint the whale meat.
Like the Japanese, the Sea Shepherd Conservation Society is collecting video evidence of the action at sea and Mr Watson is not worried about prosecution.
"Well, they're criminals. We've been down here for five years and haven't been charged with any crime. They're the ones that are poaching - they're no different than elephant poachers and we're trying to stop their illegal activities."
He said the conflict between the parties is becoming increasingly aggressive.
NZ opposed to whale hunt
The New Zealand and Australian governments oppose the Japanese whale hunt, but have called on whalers and anti-whalers to remain peaceful in the dangerous Southern Ocean.
The annual Japanese whale hunt is aimed at catching about 900 whales.
Although Japan officially stopped whaling under a 1986 global moratorium, it continues to take hundreds of whales under a loophole allowing whaling for research purposes.
Much of the meat ends up on supermarket shelves and dinner tables.