New Zealand has warned that the mood between Japanese whalers and protesters who challenge them annually off Antarctica is especially volatile this year, and urged both sides to show restraint to ensure no one is killed.

The whalers left Japan earlier this month for the Antarctic Ocean, and the Sea Shepherd Conservation Society boats have left New Zealand in pursuit.

Each year, the Sea Shepherd protesters try to harass the whaling fleet into stopping a hunt that Japan says is part of a scientific programme and not subject to a moratorium on commercial killing of the mammals.

Clashes often follow, and in January a Sea Shepherd boat was sunk after its bow was sheared off in a collision with a whaling ship.

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