SYDNEY - A GREENPEACE protest vessel has chased a fleet of Japanese whalers out of their Southern Ocean hunting grounds, the environmental group said on Sunday.

Greenpeace said its ship Esperanza pursued the lead Japanese boat, the Nisshin Maru, for 24 hours and over hundreds of kilometres before it left the area in which it is taking part in the slaughter of 1,000 whales.

'We came here to stop the fleet from whaling and we have done that. Now they are out of the hunting grounds they should stay out,' Greenpeace Japan campaigner Sakyo Noda said in a statement.

Greenpeace and other environmental activists are tracking the Japanese fleet hunting in the waters off Antarctica to prevent the whales being slaughtered.

Tokyo says the kill is for scientific research, exploiting a loophole in a 1986 moratorium on whaling, but makes no secret of the fact that the meat ends up on Japanese supermarket shelves.

Australia's Labour government, which opposes the hunt, has urged the activists to exercise restraint while on the high seas and said it will use the Customs ship Oceanic Viking to gather evidence for a potential international court case against Tokyo.

But the conservative opposition has described the Oceanic Viking as a 'ghost ship' which has yet to reach the Japanese fleet.

'It's almost a month since Labor promised that Oceanic Viking would be out on the high seas - weeks and weeks later the ship has still not caught up with the Japanese fleet,' opposition environment spokesman Greg Hunt said.

'If you make a bold promise to the world and don't keep it, it sends a message to the Japanese that we are only kidding, we weren't serious and we were just playing a domestic game.'

A spokeswoman for the government said the ship was on course but refused to give details on its operation.

'We're on track to collect photographic and video evidence of Japan's actions - that's the mission of the Viking and we are on track to do so,' a spokeswoman for Home Affairs Minister Bob Debus said. -- AFP