Prime Minister John Key says Japan is wrong to send whaling vessels to the Southern Ocean.
Japanese media have reported a whaling fleet left the southwestern city of Shimonoseki yesterday to catch 333 Antarctic minke whales.
Speaking before the Apec summit in Peru, Mr Key said New Zealand had taken a strong stand against whaling and was supported by the International Whaling Commission.
He said the hunt was not legitimate.
The fleet's stated aim would be to catch Minke whales for scientific purposes, although the International Court of Justice has debunked that reasoning.
The latest fleet follows a similar mission last year, in which the whalers evaded protest boats.
Earlier efforts produced fierce clashes at sea with anti-whaling group Sea Shepherd.
The Japan Times reported the target catch was 333 minke whales.
It said two whaling vessels - the Yushin Maru and Yushin Maru No 2 - left port yesterday.
They will be joined by two other whaling ships and the massive "mother ship" Nisshin Maru.
There will be 185 crew members in total.
Foreign Affairs Minister Murray McCully has also deplored the move.