Fisheries Minister Ian Macdonald said an Australian fisheries patrol boat will monitor the actions of the six vessels, which are flying the flags of Georgia and the west African nation Togo, but will not stop them fishing.

Macdonald said the boats would not be in the Southern Ocean unless they were fishing for the protected and increasingly rare Patagonian toothfish.

But because Georgia and Togo are not signatories to the Convention on the Conservation of Antarctic Marine Living Resources, which regulates fishing in the region, they are not bound by its rules.

"The evidence we get from our captain and crew of the (patrol boat) Oceanic Viking is that they are fishing and taking Patagonian toothfish," Macdonald told ABC radio.

"The difficulty for the Australian vessel is that under international law as it currently is, they are not doing anything illegal.

"But responsible fishing nations have actually stopped fishing in that area because of concern about the stocks of Patagonian toothfish."

Canberra has contacted Georgia and Togo about the ships and will press for more regulation to prevent poaching in the Southern Ocean at two upcoming international conferences, the minister said.

"These vessels from rogue nations -- flags of convenience nations -- are simply ignoring the problems of sustainability, the environmental problems and are fishing without any limitation whatsoever," he said.

The Patagonian toothfish fetches high prices in the United States and Japan but experts have warned it faces extinction if illegal fishing is not curbed. Some 32,000 tonnes of the species were caught illegally in 1997-1998, according to the government.

In 2003, a Uruguayan-registered fishing vessel was escorted into a Western Australian port after being captured in the South Atlantic ocean following a 21-day pursuit. The boat had 90 tonnes of Patagonian toothfish aboard.

A second Uruguayan boat was later caught carrying 150 tonnes of the species valued at more than two million dollars (1.5 million US).