A Greenpeace spokesperson told Radio Netherlands Worldwide that they were there to protest Shell's drilling around the North Pole. They did not inform the police or the city of the protest beforehand, the spokesperson added.
Police said those arrested would be released as soon as possible.
Protesters built a wall of fake oil and blocks of ice, the spokesperson said. One protester dressed as a polar bear climbed the Shell building and hung a banner.
Greenpeace believes Shell's drilling operation near the North Pole is risky, with an oil leak nearly impossible to stop or clean up due to extreme weather conditions.