A conservationist group's boat that was chasing a Japanese whaling vessel off Antarctica was seriously damaged by a giant wave today - a major setback in the group's ongoing and sometimes violent battle with Japan's whaling fleet, the activists said.

The wave cracked the hull and severely damaged one of the pontoons on the Brigitte Bardot, a scout vessel for the Sea Shepherd Conservation Society, which is chasing the whaling fleet in the hopes of interrupting Japan's annual hunt.

None of the boat's 10 crew were hurt, and the vessel was in no danger of sinking in the icy waters, Sea Shepherd founder Paul Watson said.

"It's not going to stop our attempt, but it is a setback because it takes out one of our boats," Mr Watson said by phone from his vessel, the Steve Irwin.

The Brigitte Bardot was chasing the Japanese ship Nisshin Maru in 20-foot swells when the rogue wave smashed into the port side of the vessel, cracking the hull, Mr Watson said. The pontoon was in danger of breaking off, but the boat was not taking on any water, he said.

"The captain there assures me that everything will be fine by the time we reach them," Mr Watson said.

The Steve Irwin, named after the late Australian crocodile hunter, was making its way through rough seas toward the Brigitte Bardot and was about 12 hours away, Mr Watson said.

Once there, the Steve Irwin will escort the stricken boat 1,500 miles to Fremantle, Western Australia, for repairs, and immediately return to the waters off Antarctica to continue chasing the whalers.

Meanwhile, the group's third vessel, the Bob Barker, was left to hunt the whaling fleet by itself.