Heroes star Hayden Panettiere has been involved in an aggressive confrontation with Japanese fisherman as she tried to upset their annual dolphin slaughter.

Video footage shows the 18-year-old - along with six surfers from Australia and the U.S. - paddling out into open sea to try and rescue a pod of trapped dolphins who were moments away from being killed.

However their efforts were quickly interrupted by a fishing boat and they were ushered back to shore - with one fisherman threatening them with a fishing hook.

Panettiere – who is a committed marine conservationist and supporter of the campaign to save the Japan dolphins - later spoke of her distress. 

"It was really frightening" she told Sky News "Some of us were hit by the boathook. But in the end all we really worried about was the dolphins.

"It was so incredibly sad. We were so close to them and they were sky hopping, jumping out of the water to see us."

She quickly broke down into tears saying: "One little baby dolphin stuck his head out and kinda looked at me and the thought that it's no longer with us is really hard to take."

Panettiere along with the five other surfers quickly drove to Osaka airport where they left the country immediately to avoid arrest.