But the Japanese have been unable to shake off the protesters, who have been harassing them since finding the fleet earlier this week, Shane Rattenbury told AFP by satellite phone from one of Greenpeace's two ships in the area.

"Right now we are chasing the Japanese whaling fleet. About 5:00 pm yesterday the fleet got into formation and started travelling north at high speed, which is uncharacteristic.

"They've continued all through the night and all through the day today and there's actually no whaling taking place. It appears that the fleet is on the run and trying to shake us off," he said.

"Historically they've been able to do that because we've not had fast enough vessels, but this time we've brought our newest ship, Esperanza, which was specifically bought for this purpose and we have enough speed to keep up with the fleet so they're not managing to get away from us."

On Thursday, Rattenbury said, activists in small inflatable boats had repeatedly manoeuvred into position between target whales and the harpooners, allowing several whales to escape.

"So far the harpoonists haven't fired at the inflatable boats and when the inflatables got in the way they've been forced to not take the shot, which is what's enabled the whales to escape.

"So we believe it's the most effective tactic we have in terms of non-violent protest. All our crew down here are very passionate and willing to take the risk involved in that to defend the whales."

On Wednesday, Japanese ships used fire hoses against Greenpeace inflatables which approached, but the smaller "catchers" were unable to do so, Rattenbury said.

There was also a minor collision between a Japanese vessel trying to unload a dead whale and a Greenpeace ship blocking access to the factory ship, leading Japan to denounce the group's tactics as akin to "piracy".

"Where they were yesterday was an area where the hunting was very good, so it seems odd for them to have moved away from that area," Rattenbury said in support of his claim that the fleet was on the run.

"They were successful harpooning some whales despite our best efforts. That in itself is quite a traumatic process to watch as the whales tend to take some time to die, so they're thrashing in the water and trying to escape."

The Greenpeace boats, the Esperanza and the Arctic Sunrise, with a total of 57 crew on board, would continue to harass the Japanese fleet for several weeks, Rattenbury said.

Protesters on land are also expected to turn out to meet one of the Japanese boats when it docks in Hobart in Tasmania to deliver a crewman with appendicitis to hospital on Saturday, he said.

Greenpeace has called on the Australian government to refuse to refuel the ship and thus prevent it from returning to the hunting grounds.

The government, while reiterating its opposition to whaling, has turned down the request.

Japan says it conducts whale hunts for scientific research, but critics say that is a cover for commercial killing of whales for consumption in Japan, where whalemeat is popular.

Despite international protests, Japan has this year more than doubled its planned catch of minke whales to 935 and added 10 endangered fin whales.

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