Australia and New Zealand on Tuesday applauded a court decision that Japan must halt its annual Antarctic whale hunt, but raised fears it could sidestep the order and begin whaling again under a new "scientific" guise.

The United Nations' Hague-based International Court of Justice (ICJ) ruled on Monday that Japan's whaling programme was a commercial activity disguised as science, and said it must revoke existing whaling licences.

A "deeply disappointed" Tokyo said it would honour the ruling but did not exclude the possibility of future whaling programmes, with New Zealand expressing concerns Japan may try to circumvent the order.

"The ICJ decision sinks a giant harpoon into the legality of Japan's whaling programme," New Zealand Foreign Minister Murray McCully said.

"It still does leave Japan with a decision to make after they've digested this, which is to look at whether they try to devise a new programme that is scientifically based that they could embark upon whaling in the Southern Ocean again.

"Our task is to make sure that we carry out a diplomatic conversation that dissuades them from embarking on that course."

A Japanese minister on Tuesday defended whaling -- seen by some as an important cultural practice -- but stopped short of detailing what next steps Japan would take.

"Whale meat is an important source of food, and the government's position to use it based on scientific facts has not changed," Agriculture, Forestry and Fisheries Minister Yoshimasa Hayashi told a press conference.

"We will scrutinise the verdict and study (measures to be taken) swiftly," he said according to the Jiji news agency. Japan also has a coastal whaling programme which is not covered by the ban.

Australia, backed by New Zealand, hauled Japan before the ICJ in 2010 in a bid to end the annual Southern Ocean hunt.

Tokyo has long been accused of exploiting a legal loophole in the 1986 ban on commercial whaling that allowed the practice to collect scientific data. Japan has killed 10,000 of the giant mammals under the scheme since 1988, Australia has alleged.

International law expert Steven Freeland, from the University of Western Sydney, said Japan could simply redesign its whaling programme to skirt the ruling. He pointed out that the ICJ confirmed scientific research can include killing whales -- just not so many.

"The problem for Japan was its failure to take proper account of non-lethal methods of research or to justify the actual catch numbers it had declared," he said.

"Japan may instead take a very close look at why its implementation of (its research programme) fell foul of its legal obligations and perhaps seek to design and ultimately implement a new whaling programme that takes into account all of those elements."

Japan had argued that its JARPA II research programme was aimed at studying the viability of whale hunting, but the ICJ found it had failed to examine ways of doing the research without killing whales, or at least while killing fewer of them.

Masayuki Komatsu, a former head negotiator for Japan on the whaling issue, said Tokyo had been a victim of its own lax approach over the last decade.

"It became clear in the court procedure and hearings... that Japan was not ambitious enough about its scientific research as it did not catch as many whales as it needed for obtaining data," he said.

"As a result, the entire research whaling programme was judged as a commercial hunt."

A respected blogger and social commentator on Japanese issues, who goes by the name of Hikosaemon, said the narrow issue of whether or not the whaling programme was "science" largely missed the point.

"I think it is clear that both sides here... were seeking moral vindication of their positions," he told AFP.

"Even if it can fix the technical issues with its scientific whaling programme... Japan will need to weigh up whether it is worth the increasing PR damage this issue causes."

The irony, added Hikosaemon, is that the issue of whaling is itself not particularly important for many Japanese.

But efforts "to demonise Japan over this issue have galvanised a siege mentality that has transformed this from an issue about the right to hunt and eat whales, into a more fundamental issue of fair treatment among countries with different cultural values."

burs-hg/kjl/sls