Conservation Minister Steve Chadwick said the Japanese fleet was photographed by a Royal New Zealand Air Force Orion airplane during a routine surveillance flight for illegal fishers in the southern oceans.

Ms Chadwick said the Japanese whalers were heading toward the Ross Sea, an area for which New Zealand has international search and rescue responsibility.

After slaughtering whales in New Zealand's Antarctic waters last year, Japan had agreed under an International Whaling Commission protocol to hunt in Australian waters, Ms Chadwick said.

'But it looks like they're heading into our territory down there - very remote, very dangerous, very hostile territory,' she told New Zealand's National Radio.

Last year's southern ocean whale hunt by Japan ended early after it's whaling fleet factory ship, Nisshin Maru, was crippled by fire and one crew member killed in New Zealand's Ross Sea waters.

The fire left the ship drifting and without engine power for 10 days, prompting strong protests from the New Zealand government and from environmental group Greenpeace over potential oil and chemical spills or damage to nearby Antarctic penguin colonies.

Ms Chadwick said it was not illegal for the Japanese ships to go into Ross Sea waters that fall under New Zealand jurisdiction but it would breach a protocol the whalers agreed to earlier.

'We are also deeply concerned about the risk to human life and to Antarctica's pristine marine environment, should the Japanese whaling fleet encounter problems at sea,' she said.

Mr Glenn Inwood, a spokesman for Japan's Tokyo-based Institute of Cetacean Research, said he was unable to confirm where the whaling fleet was going.

'They move a large number of nautical miles a day,' he said.

Mr Inwood said New Zealand 'has no claim' on the Ross Sea area which is international waters 'and Australia has no claim on the southern oceans area' near to its land mass.

'We expect New Zealand to take a tough line in respect of protests by Sea Shepherd and Greenpeace' against Japan's legal whaling, he said.

Anti-whaling groups Sea Shepherd and Greenpeace have ships trailing the fleet and have already clashed with it ? notably when two Sea Shepherd crew boarded a whaling vessel and were held by the Japanese crew until an Australian government vessel had them released.

On Tuesday, Greenpeace environmentalists clashed with the whalers, with each sides accusing the other of dangerous tactics after Greenpeace activists failed to prevent the factory ship from refuelling.

Japan plans to slaughter nearly 1,000 whales this year as part of its scientific whale research program, dismissed by opponents as a front for continuing commercial whaling banned by the IWC in 1986. -- AP