Oil giant Shell filed a legal complaint Tuesday against Greenpeace protestors who have boarded an Arctic-bound oil rig in the middle of the Pacific Ocean, a spokeswoman said.

The six activists are camping out on the 38,000-tonne Polar Pioneer platform, which they boarded 750 miles northwest of Hawaii using inflatable boats from the Greenpeace vessel "Esperanza."

"These acts are far from peaceful demonstrations," said a Shell statement a day after confirming the Greenpeace action Monday.

"Boarding a moving vessel on the high seas is extremely dangerous and jeopardizes the safety of all concerned, including both the people working aboard and the protestors themselves," it added.

The Anglo-Dutch group said it had filed a complaint in federal court in Alaska, seeking an injunction "to end the illegal boarding currently taking place in the Pacific Ocean and to prevent such actions in the future."

The injunction "would apply while the all of the vessels associated with our Alaska exploration program are in transit to the US, while in port, and while transiting to our leases." The rig is on its way to the Arctic via Seattle, Washington.

"The injunction, if granted, would also apply to the aviation assets related to the program," it added.

The six activists -- from the United States, Germany, New Zealand, Australia, Sweden and Austria -- have supplies for several days and can communicate with the outside world, Greenpeace said.

Johno Smith, one of the protestors from New Zealand, said: "We're here to highlight that in less than 100 days Shell is going to the Arctic to drill for oil.

"This pristine environment needs protecting for future generations and all life that will call it home.

"But instead Shell's actions are exploiting the melting ice to increase a man-made disaster."