Anti-whaling group Sea Shepherd claims two of its boats were deliberately rammed by a Japanese whaling ship in the Southern Ocean.

Sea Shepherd had been trying to halt whaling in Antarctica, and this week had been blocking the whalers’ access to a Korean fuel tanker, Sun Laurel.

Paul Watson from Sea Shepherd said it had been a successful strategy for around 48 hours, but then the factory ship Nisshin Maru came in.

“They hit the Steve Irwin twice in the stern and then moved in on the Bob Barker, hitting it multiple times and slamming it into the side of the tanker.”

“Then they lost control and slammed into the back side of their own tanker, causing some structural damage and destroying their lifeboat.”

Watson said the fuel tanker hit by Nisshin Maru sent Sea Shepherd a message in a bottle to say it did not support how the Japanese were dealing with the situation.

He said Nisshin Maru staff were throwing stun grenades, and hitting Sea Shepherd members with high-powered water cannons.

Bob Barker skipper Peter Hammarstedt said there was a moment when the Nisshin Maru came in, and he could not get out of the way.  

 “I looked out my bridge window to starboard and all I could see was Nisshin Maru’s anchor, a vessel five times my size.

“As they started pushing us, my biggest fear was that they would push us over - and we have 35 souls on board.”

Hammarstedt said the Japanese ship hit them several times before pulling away.

“They realised they could either back off or kill everybody aboard ship.”

Hammarstedt said a mayday distress call was made as he believed his boat was going to roll over.

“We sustained structural damage to the ship, but we are afloat, we do have propulsion and we have withdrawn our mayday.”

The structural damage is above the waterline.

“I have lost a lot of communications equipment to the anchor of the Nisshin Maru.”

No one was hurt on the Bob Barker.

The whaling fleet has moved north with the Sea Shepherd fleet in pursuit.

Captain Siddharth Chakravarty, aboard the Steve Irwin, has said the situation had gone too far.

“The recklessness of the Japanese whaling fleet and the Sun Laurel have put Antarctica's rich environment at grave risk for an ecological nightmare,” he said.

“The time has come for the Australian government to intervene and put a stop to this insanity."

In an earlier statement Sea Shepherd said it had observed the Sun Laurel leaking oil into Australian Antarctic Territorial waters. It said this was a breach of Australian and international law.

Sea Shepherd also claimed the Nisshin Maru was attempting to take fuel from the Sun Laurel in these waters, also a breach of law.

- © Fairfax NZ News