Two anti-whaling activists taken hostage by Japanese whalers in Antarctica earlier this week have been freed and are now on the Australian ship the Oceanic Viking, the Sea Shepherd protest organization said Friday.

Australian Benjamin Potts, 28, and Briton Giles Lane, 35, were detained since they risked their lives boarding a Japanese harpoon vessel on Tuesday to deliver an anti-whaling protest.

A stalemate that developed with the Japanese refusing to release their hostages until Sea Shepherd agreed to stop harassing the whaling fleet was broken when Australia interceded with an offer to take the pair off and later transfer them to the Sea Shepherd vessel the Steve Irwin.

The Oceanic Viking is a Customs ship sent by Canberra to monitor the Japanese whaling fleet.

Transferring the pair to the Oceanic Viking before returning them to the Steve Irwin means Potts and Lane avoided a possible piracy charge when they reached Japan.

The ships were more than 4,000 kilometres south-west of Perth on Australia's west coast early Friday.

Sea Shepherd executive director Kim McCoy told Australia's ABC Radio that the pair were on the Oceanic Viking and would be back on the Steve Irwin within hours.

"We received confirmation, and I've since spoken with one of the hostages, who are no longer being held hostage, on board the Ocean Viking, and he confirmed that they're both completely safe," she said.

"They're on the Oceanic Viking and they're just going to give them a place to sleep until we can pick them up in the morning at a rendezvous point," she said.

Glenn Inwood, spokesman for the Japanese, told Radio New Zealand that the whaling fleet, which is on its annual hunt for nearly 1,000 whales for a so-called research programme, would now resume whaling.

"It was certainly quite handy for the Japanese government that the (Oceanic Viking) was there because it helped them resolve the situation with the two illegal intruders," Inwood said.

"It became very clear yesterday after 24 hours of receiving no communication from the Sea Shepherd organization that they had no intention of removing the men from the Japanese vessel and therefore the Australian government was asked to intervene and take them aboard their Customs vessel," he said.