"Xena: Warrior Princess" actress Lucy Lawless pleaded guilty in a New Zealand court Thursday to unlawfully boarding a ship in protest at plans to search for oil off Alaska.

The actress said she had no regrets about joining a group of Greenpeace activists who occupied the oil-drilling ship Noble Discoverer for three days in February in a bid to prevent it sailing from New Zealand to the Arctic and searching for oil.

The protest at the North Island port of Taranaki ended peacefully when police arrested the demonstrators after scaling a 53-metre (174-foot) drilling derrick on the ship, which is contracted to Anglo-Dutch energy giant Shell.

Eight activists, including Lawless, were initially charged with burglary but pleaded guilty in Auckland District Court Thursday after the charges were downgraded to unlawfully boarding a ship.

Lawless, who appeared in court under her married name Lucy Tapert, said the protest had successfully drawn attention to the issue and prompted 470,000 people to sign an online campaign opposing deep sea drilling.

"Certainly I stand by what we did and our need to do it," she told reporters outside the court, adding "I had to do what I had to do".

"Peaceful action is the only way forward, a clean green Earth is what we need."

She said while the possibility of a conviction may be damaging for her career "it's not as risky as doing nothing".

Lawless, who starred as the title character in the fantasy television series "Xena: Warrior Princess" from 1995-2001, is a long-time environmental activist who was named a Greenpeace ambassador in 2009.

She and the other activists will be sentenced on September 14, when they will apply for the matter to be discharged without conviction.

The Noble Discoverer has since set sail for the Arctic.

The US Interior Department granted Shell conditional provisional approval to begin drilling exploration wells in the Arctic Ocean last August, in a move slammed by conservationists.

US officials had pledged to closely monitor Shell's plans for four shallow water exploration wells in Alaska's Beaufort Sea to ensure operations are conducted in a "safe and environmentally responsible manner".

But green groups say it puts wildlife and native communities in the remote region at risk, citing the vastly complicated task of drilling in the harsh Arctic environment and effectively cleaning up any spills in such conditions.

They also point to the environmental catastrophe in the Gulf of Mexico in 2010 after Shell's Deepwater Horizon rig exploded as an example of the risks inherent in drilling for oil.