Environmental group Sea Shepherd claims to be closing in on the Japanese whaling fleet after spotting four ships in the Southern Ocean.
The anti-whaling activists say their boats will intercept the fleet in the Ross Dependency Antarctic region.
Sea Shepherd's helicopter flew over the area and found Japan's factory processing ship, the Nisshin Maru, and three harpoon vessels just before 5am (AEDT) on Sunday.
Steve Irwin captain Siddharth Chakravarty says it's the third time this year their helicopter has been successful in finding the whalers.
"We are proud that today is a day that we have seized for the whales, restoring peace to the Southern Ocean Whale Sanctuary," he said in a statement.
The group says it plans on sailing right behind the main factory ship to prevent whales being hauled in from the sea.
Japan's Institute of Cetacean Research has been contacted for comment.