There is little sympathy from an Australian maritime law expert for two activists being held on board a Japanese whaling vessel in the Southern Ocean.

The Australian and Briton from the Sea Shepherd vessel Steve Irwin illegally boarded the Yushin Marun No2 last night.

Professor Sam Bateman says the men committed an act of piracy and the Japanese have every right to detain them.

The Japanese Government has ordered the whalers to release the men, however they say the protesters are avoiding them and are preventing a hand over.

Cetacean Research is denying whalers roughed up the two activists. Colleagues on the Sea Shepherd protest vessel Steve Irwin claim the two men were also tied to a mast in freezing weather for three hours.

But Cetacean Research Institute spokesman Glenn Inwood says none of the claims are true. He says the whalers were left with little option but to detain them after they tried to cripple the Yushin Maru by entangling ropes around her anchor.

New Zealand's representative on the International Whaling Commission Sir Geoffrey Palmer is calling for cool heads to prevail to resolve the standoff. He is calling for some kind of diplomatic solution involving the consular's of Australia and Britain.

The Government says protestors heading to the Southern Ocean to protest Japanese whalers are aware of the risks they are taking. Duty Minister Rick Barker says they are concerned with what has happened, and hope it can be resolved without further confrontation.

Mr Barker says any acts of provocation that could endanger lives in the Southern Ocean should be avoided.

He says New Zealand will consider any request for help it gets from Australian authorities.