Over a dozen people were detained after Greenpeace activists blocked access to Shell headquarters Friday to protest against the oil giant's plans to drill in the Arctic, local police said.

"We showed up in a group of 70 around 7 o'clock this morning and we blocked all entrances to stop employees from getting to their offices and continuing work on the Arctic drilling," Greenpeace spokeswoman Ilse van der Poel told AFP.

The environmental group said a total of 70 activists took part in the protest Friday morning at the Anglo-Dutch company building, but police spokesman Cor Spruit put the number at 30.

He said police detained 13 people and they were expected to be released over the course of the day.

"Four of them were inside the building," he said, adding that the other nine were those who were on the roof or had climbed up to hang a banner across the front of the headquarters.

According to van der Poel, nine Greenpeace climbers had hung a "Stop Shell, Save The Arctic" banner across the building and also attempted to dismantle the Shell logo to replace it with one of a polar bear.

She added that Greenpeace director Sylvia Borren went to occupy the office of Shell CEO Peter Voser in the protest, which voluntarily came to an end at 0630 GMT (8:30 am).

The protest comes after Greenpeace launched a Save The Arctic campaign last month to preserve the land mass from oil exploration and industrial fishing.

In May, the group's activists temporarily halted several icebreakers headed for the Arctic in a bid to block Shell's plans to drill for oil in the region.

And last month the environmental group called for more use of renewable energy and greener cars in what it said would help protect the Arctic and other areas from being spoiled by oil drilling.

"There would be no need to exploit the Arctic and other marginal sources of oil, such as the tar sands in Canada and offshore oil in Brazil, if more renewable energy powered our vehicles and if much stronger efficiency standards for cars were adopted in Europe and elsewhere," the group said in a statement.

According to the US Geological Survey, the Arctic is believed to hold 13 percent of the planet's undiscovered oil reserves and 30 percent of its undiscovered natural gas.