Chadwick said it was not illegal for the Japanese ships to enter Ross Sea where New Zealand has international search and rescue responsibility, but the act would be a breach of the agreed protocol.
"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."
Last year, Japan's southern ocean whaling season ended early after its factory ship, Nishin Maru, was crippled by fire while hunting in the Ross Sea area killing one crew member.
Commenting on New Zealand's claims Glenn Inwood, a spokesman for Japan's Institute of Cetacean Research, said he could not confirm where the whaling fleet was heading.
He said neither New Zealand nor Australia had a claim to any area in the Ross Sea or the southern oceans, which he said were international waters.
But he added that officials should take a firm stand over the tactics of anti-whaling protesters looking to disrupt the Japanese hunt.
"We expect New Zealand to take a tough line in respect of protests by Sea Shepherd and Greenpeace."
Both groups have ships trailing the Japanese whaling fleet, hoping to disrupt the whale hunt and prevent whales from being killed.
In a recent incident, two Sea Shepherd crew members boarded a whaling ship and were held by the Japanese crew until an Australian government vessel picked them up.
Environmentalists have clashed with Japanese
whalers this season [Photo: Greenpeace]
Earlier this week Japan's prime minister defended his country's whale-hunting programme saying it was part of scientific research.
Referring to the recent clash with anti-whaling activists he said it was wrong to get emotional about the issue.
"Should that lead to more emotionally charged debate, then I feel that would be very unfortunate," he told the BBC in an interview on Wednesday.
"So we should try to continue with our efforts to try to explain that we are engaged in this research whaling activity from a scientific viewpoint."