The anti-whaling group Sea Shepherd Conservation Society says its inflatable craft have been deluged with water cannon fired by crew on Japanese whaling ships in the Southern Ocean.
Sea Shepherd's founder Paul Watson says his three-strong fleet was able to locate a Japanese whaling group before it could start catching whales.
He says at first the whalers tried to elude the protest fleet, which in turn pursued them.
But about midday on Saturday, the situation changed when the protesters were able to approach the whalers' factory ship Nisshin Maru.
Then inflatables launched by the protest fleet were able to get between three Japanese harpoon vessels and the factory ship.
At that point, Mr Watson says the Japanese fired water cannon at the protesters who in turn flung stink bombs onto the decks of the Japanese ships.
Later, Mr Watson says the protest fleet set out to chase the Nisshin Maru and were themselves pursued by the Japanese harpooners.
This action took place around midday on Saturday amid ice floes 3000km south-east of New Zealand.