The captain of a conservation ship clashing with Japanese whalers in the Southern Ocean has labelled the New Zealand Government "contemptible" for allowing Japan to continue killing whales.

Paul Watson, of the Sea Shepherd vessel Farley Mowat, was today criticised by Conservation Minister Chris Carter as irresponsible for using tactics such as running into whaling ships with a "can opener" device in a bid to stop them taking whales.

Capt Watson said such criticism was unfounded.

"If the Australian government and the New Zealand Government were acting responsibly then we wouldn't be down here," he said from aboard his vessel in the Southern Ocean.

"The fact is the Japanese whaling fleet is in blatant violation of international law and nobody is doing anything about it.

"We're not here to protest, we're down here to uphold international conservation law and to chase these guys out of here and it's working. They're afraid of us and we want them to be afraid of us. "

Mr Carter today condemned the Sea Shepherd actions.

"The increasing anxiety that the Japanese are showing is partly a response to the very irresponsible behaviour by Paul Watson from the Sea Shepherd group," he said.

But Capt Watson, a Canadian-born United States resident, said if anybody was irresponsible, it was not Sea Shepherd.

"If the New Zealand Government is concerned about it, then hey, send a navy vessel down here and check it out. Keep an eye on things and act responsibly."

He said the Australian and New Zealand governments were "contemptible" in allowing the whaling to continue.

"I think they're kissing the rear ends of Japan, is what I think. If these were Indonesian fishermen, Australia would be very aggressive about it.

"There's no difference between illegal poaching by Indonesia and poaching by Japan."

A spokesman for Mr Carter said the minister did not want to make any further comment.

Capt Watson admitted there was "always a risk" in any action at sea, but in his experience, dating back to 1977, he had never caused an injury to anybody.

He was acting under the United Nations World Charter for Nature, which he said stated non-government organisations could use powers to uphold international conservation law, a defence which had previously seen him acquitted by a jury in Canada in 1995 for "chasing" Spanish drag trawlers.

The Japan Whaling Association's president Keiichi Nakajima yesterday labelled Sea Shepherd "dangerous vegans" and "circus performers".

The Government has asked the New Zealand Air Force to keep an eye out for whaling vessels in the Southern Ocean as its Orion aircraft conduct routine checks for illegal fishing in the area.

Air force spokeswoman Danielle Coe today said an Orion crew spotted a whaling fleet on at least one occasion before Christmas, but the fleet had since moved out of the area being monitored.

The Green Party has called for the Government to send a navy frigate to monitor events between the whalers, Sea Shepherd, and Greenpeace.

But Mr Carter today said a navy frigate could not be sent as it would have no legal standing and might inflame the situation as New Zealand was seen as strongly conservationist.

Greenpeace, which is committed to non-violent action, has distanced itself from Sea Shepherd which Capt Watson established in the 1970s when he quit Greenpeace -- an organisation he helped set up.