View from the Farley Mowat as it 'sideswipes' the Japanese ship. Picture / Sea Shepherd

View from the Farley Mowat as it 'sideswipes' the Japanese ship. Picture / Sea Shepherd

Anti-whaling activists in Antarctica claim to have deliberately collided with a supply vessel of the Japanese whaling fleet.

Paul Watson, leader of the Sea Shepherd Conservation Society, says his ship, Farley Mowat, "sideswiped" the tanker Oriental Bluebird at 1.30pm Monday (NZ time).

Sea Shepherd, along with fellow conservationists Greenpeace, say the Oriental Bluebird is being used to refuel six Japanese whaling ships as well as to carry refrigerated whale meat, collected as part of Japan's so-called scientific research whaling.

Watson said he ordered the supply ship to leave the Antarctic Whale Sanctuary as it was waiting to rendezvous with the whaling factory ship Nisshin Maru.

"I informed the Oriental Bluebird that I was acting under the authority of the United Nations World Charter for Nature to uphold international conservation regulations prohibiting the slaughter of whales in the Antarctic Whale Sanctuary.

"When they refused, we backed up the message by slamming our starboard hull against their starboard hull."

Watson said there was no damage apparent to either ship aside from a long scratch along the hull of the Oriental Bluebird caused by a heavy steel blade attached to the Farley Mowat's hull known as the "can opener". No injuries were reported.

He said the blow was meant to convey the seriousness of his demand that the Japanese whalers leave the area.

"After the collision, the Oriental Bluebird began running with the Farley Mowat in pursuit."

On the stern and starboard side of the Oriental Bluebird are the words "whale meat" painted on the ship by Greenpeace activists on Sunday.

Watson said he believes the Japanese are killing more whales than the factory ship can carry, so it is essential for the whalers to offload meat in order to continue.

"There is simply not enough room on the Nisshin Maru for 935 minke whales and 10 fin whales."

Watson described the Panama-registered Oriental Bluebird as flying a flag of convenience while being operated by New Shipping Kaisha Ltd, of Tokyo.