New Zealand will express its "significant disappointment" to Japan over the country's whaling in the Southern Ocean, Prime Minister Bill English says.

"I think our view is pretty well known and we would take the same sort of view as Australia on this," said English, who is on his way home from his first trip to Europe as Prime Minister.

"The issue has just arisen, and New Zealand will be expressing its significant disappointment about what is going on there."

The activist group Sea Shepherd on the weekend published a photo it said showed a Japanese whaler in the Australian Whale Sanctuary with a dead minke whale on its deck.

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The International Court of Justice ruled against Japan's whaling operations in the Southern Ocean in 2014. That case was brought by Australia.

On Monday Australian Environment Minister Josh Frydenberg expressed "deep disappointment" that Japan had decided to return to the Southern Ocean to undertake so-called "scientific" whaling.

New Zealand would support Australia on the issue through the appropriate channels, English said.

"We are on the international whaling commission, we have ongoing diplomatic discussions with Japan."

New Zealand had worked for years to protect whales and engage with Japan to try and change their attitude, he said.

"That hasn't been successful yet, so that is disappointing."

English said he did not know if Japan's actions were deliberately provocative.