The Antarctic whaling conflict appears to have taken a dangerous turn, with claims Japanese ships attempted to sabotage Sea Shepherd vessels in the ice-strewn Ross Sea.

Ships from the two sides collided on Sunday, and Japanese harpoon ships are said to have tried repeatedly to foul the propellors of the acivists' ships with steel cables and rope.

Despite the clashes, Sea Shepherd's Peter Hammarstedt said the activists were still in contact with the fleeing Japanese factory ship, Nisshin Maru.

Hammarstedt said his ship Bob Barker and the Steve Irwin were following the Nisshin Maru for the eighth day, preventing it from whaling, at a distance of about two nautical miles when a concerted attack began.

"We haven't experienced such a ruthless and co-ordinated attack out of the blue like this before," Hammarstedt said.

Three Japanese harpoon boats trailing 300 metre lengths of steel cable and ropes made repeated close passes over the bows of the Sea Shepherd ships, he said.

"They managed to entangle the propellor of the Steve Irwin with a rope, but the prop cut it free," he said.

"Then in one of the passes the Yushin Maru No 2 hit the bow of the Bob Barker as it crossed in front."

He said his ship has sustained buckled bow plates. "They damn near took my anchor off and it's now dangling free like a wrecking ball."

The engagement forced the Bob Barker to slow, and it had lost contact with the Nisshin Maru, he said.

"The Steve Irwin still has Nisshin Maru on its radar, and it has a helicopter which can track the ship too."

Hammarstedt said he reported the collision to Maritime New Zealand's Rescue Co-ordination Centre, but his vessel did not need assistance, and none of his crew had been injured.

Comment on the incident was being sought from the Japanese Government. It has repeatedly warned against what it says are the obstructive activities of Sea Shepherd.

In January, Japan protested to the government of the Netherlands as the flag state of the Steve Irwin, over an attack on the whalers' security ship, Shonan Maru No. 2

The Steve Irwin deployed two small boats whose crew trailed lines in a bid to slow down the Shonan Maru No. 2.

"When this was met with aggression from the crew of the Shonan Maru No. 2, in terms of throwing grappling hooks at the small boats and hitting two of the crew members, as well as attempts to jab the crew with long poles, I retrieved the small boats," Steve Irwin's captain, Sid Chakravaty said.